(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "The life of Crustacea"

] THE LIFE OF 
CRUSTACEA 

W.T.CALMAN 







CD 

m 

o 



THE LIFE OF CRUSTACEA 



THE 
LIFE OF CRUSTACEA 

BY 
W. T. GALMAN, D.Sc. 



WITH THIRTY-TWO PLATES AND EIGHTY-FIVE FIGURES 



METHUEN & CO. LTD. 

36 ESSEX STREET W.C. 

LONDON 



First Published in igu 




sketch of the Natural History of the 
Crustacea deals chiefly with their habits and 
modes of life, and attempts to provide, for readers 
unfamiliar with the technicalities of Zoology, an 
account of some of the more important scientific 
problems suggested by a study of the living animals 
in relation to their environment. 

I am indebted to the Trustees of the British 
Museum for leave to reproduce certain figures pre- 
pared for the " Guide to the Crustacea, Arachnida, 
Onychophora, and Myriopoda exhibited in the 
Department of Zoology "; also to Sir Ray Lan- 
kester, K.C.B., F.R.S., and to Messrs. A. and C. 
Black for the use of a number of figures from my 
volume on Crustacea in the "Treatise on Zoology," 
edited by Sir Ray Lankester. 



vi THE LIFE OF CRUSTACEA 

The source of these figures is indicated in the 
explanation attached to each. Of the remaining 
illustrations, some are reproduced from photographs 
of specimens in the collection of the British 
Museum ; the others have been drawn from Nature, 
or copied from the original figures of various authors, 
by Miss Gertrude M. Woodward, to whom I am 
much indebted for the care and skill which she has 

given to their preparation. 

W. T. C. 



CONTENTS 

CHAPTER PAGE 

I. INTRODUCTORY - - i 

II. THE LOBSTER AS A TYPE OF CRUSTACEA 6 

III. THE CLASSIFICATION OF CRUSTACEA - - 34 

IV. THE METAMORPHOSES OF CRUSTACEA - - 66 
V. CRUSTACEA OF THE SEASHORE - - 88 

VI. CRUSTACEA OF THE DEEP SEA - - 117 

VII. FLOATING CRUSTACEA OF THE OPEN SEA 138 

VIII. CRUSTACEA OF FRESH WATERS - 157 

IX. CRUSTACEA OF THE LAND - 188 

X. CRUSTACEA AS PARASITES AND MESSMATES - - 207 

XI. CRUSTACEA IN RELATION TO MAN - 237 

XII. CRUSTACEA OF THE PAST - 256 

APPENDIX : 

I. METHODS OF COLLECTING AND PRESERVING CRUS- 
TACEA - - - 271 
II. NOTES ON BOOKS - - - 277 

INDEX ........ 280 



vu 



LIST OF ILLUSTRATIONS 
IN THE TEXT 

FIG. PAGE 

1. THE COMMON LOBSTER (Homarus gammarus), FEMALE, 

FROM THE SIDE - 7 

2. ONE OF THE ABDOMINAL SOMITES OF THE LOBSTER, WITH 

ITS APPENDAGES, SEPARATED AND VIEWED FROM IN 

FRONT - - 9 

3. THIRD MAXILLIPED OF LOBSTER - - n 

4. V^ALKING LEGS OF LOBSTER - 12 
APPENDAGES OF LOBSTER IN FRONT OF THIRD MAXIL- 
LIPED 13 

6. DISSECTION OF MALE LOBSTER, FROM THE SIDE - 16 

7. GILLS OF THE LOBSTER, EXPOSED BY CUTTING AWAY THE 

SIDE-FLAP OF THE CARAPACE (BRANCHIOSTEGITE) - 18 

8. FIRST LARVAL STAGE OF THE COMMON LOBSTER, x 4 - 28 

9. SIDE - VIEW OF ROSTRUM OF (A) COMMON LOBSTER 

(Homarus gammarus) AND (B) AMERICAN LOBSTER 
(Homarus americanus) - - 32 

10. THE " FAIRY SHRIMP " (Chirocephalus diaphanus), MALE. 

x 2 - 35 

11. Estheria obliqua, ONE OF THE CONCHOSTRACA - - 36 

12. Daphnia pulex, A COMMON SPECIES OF "WATER-FLEA." 

MUCH ENLARGED - - 37 

13. SHELLS OF OSTRACODA. MUCH ENLARGED - 38 

14. Cyclops albidus, \ SPECIES OF COPEPOD FOUND IN FRESH 

WATER - - 39 

15. Nebalia bipes. ENLARGED - - 44 

16. Mysis relicta, ONE OF THE MYSIDACEA. ENLARGED 47 

17. Gnathophausia willemoesii, ONE OF THE DEEP-SEA MYSI- 

DACEA. HALF NATURAL SIZE - - 48 

8. Diastylis goodsiri, ONE OF THE CUMACEA. ENLARGED - 49 

ix 



x THE LIFE OF CRUSTACEA 

PIG. FACE 

19. Apseudes spinosus, ONE OF THE TANAIDACEA. ENLARGED 50 

20. A WOODLOUSE (Porcellio scaber), ONE OF THE ISOPODA. 

ENLARGED - - 51 

21. AN AMPHIPOD (Gammarus locusta). ENLARGED - - 53 

22. Two SPECIES OF CAPRELLIDJE - - 54 

23. Paracyamus boopis, THE WHALE-LOUSE OF THF HUMP- 

BACK WHALE - - 55 

24. Meganyctiphanes norvegica, ONE OF THE EUPHAUSIACEA. 

TWICE NATURAL SIZE - - 56 

25. LARVAL STAGES OF THE COMMON SHORE CRAB (Carcinus 

manas SEE PLATE IX.) - - - 68 

26. LAST LARVAL STAGE OF THE COMMON PORCELAIN CRAB 

(Porcellana longicornis SEE FIG. 41, P. 113). x g 70 

27. FIRST LARVAL STAGE OF Munida mgosa (SEE PLATE VI.) 

x 10 71 

28. THE PHYLLOSOMA LARVA OF THE COMMON SPINY LOBSTER 

(Palinurus vulgaris SEE PLATE V.). MUCH ENLARGED 72 

29. LARVAL STAGES OF THE PRAWN Pen&us (SEE PLATE IV.). 

x 45 -74 

30. NEWLY - HATCHED YOUNG OF A CRAYFISH (Astacus 

fluviatilis). ENLARGED - - 76 

31. YOUNG SPECIMEN OF AN AFRICAN RIVER CRAB (Potamon 

johnstont), TAKEN FROM THE ABDOMEN OF THE MOTHER. 
MUCH ENLARGED - - 78 

32. EARLY LARVAL STAGE OF A SPECIES OF SQUILLA, PROB- 

ABLY S. dubia. x 10 - - 80 

33. LARVAL STAGES OF THE BRINE SHRIMP (Artemia salina)- 81 

34. EARLY NAUPLIUS LARVA OF A COPEPOD (Cyclops). MUCH 

ENLARGED - - 82 

35. LARVAL STAGES OF THE COMMON ROCK BARNACLE 

(Balanus balanoidesSEE PLATE III.) 83 

36. A COMMON HERMIT CRAB (Eupagurus bernhardus) REMOVED 

FROM THE SHELL- - 91 

37. Pylocheles miersii, A SYMMETRICAL HERMIT CRAB - - 94 

38. Callianassa stebbingi (FEMALE), A SAND - BURROWING 

THALASSINID FROM THE SOUTH COAST OF ENGLAND. 
NATURAL SIZE - - 103 

39. THE COMMON SAND-HOPPER (Talitrus saltator), MALE, 

FROM THE SIDE, x 3 - 108 



LIST OF ILLUSTRATIONS xi 

FIG. PAGE 

40. A, A PIECE OF A TROPICAL SEA-WEED (Halimeda) ; B, A 

CRAB (Huenia protcus) WHICH LIVES AMONG THE FRONDS 
OF Halimeda, AND CLOSELY RESEMBLES THEM IN FORM 
AND COLOUR. REDUCED- - no 

41. THE COMMON PORCELAIN CRAB (Porcellana longicornis), 

SLIGHTLY ENLARGED, AND ONE OF THE THIRD MAXIL- 
LIPEDS DETACHED AND FURTHER ENLARGED TO SHOW 
THE FRINGE OF LONG HAIRS - - - 113 

42. A DEEP-SEA LOBSTER (Nephropsis stewartii), FROM THE 

BAY OF BENGAL. REDUCED - - 122 

43. Munidopsis regia, A DEEP-SEA GALATHEID FROM THE BAY 

OF BENGAL. REDUCED - - - 123 

44. Thaumastocheles zaleucus. REDUCED - 129 

45. A DEEP-SEA CRAB (Platymaia wyville-thomsoni). REDUCED 131 

46. Polycheles phosphorus, ONE OF THE ERYONIDEA, FEMALE, 

FROM THE INDIAN SEAS - - 133 

47. Eryon propinquiis, ONE OF THE FOSSIL ERYONIDEA, FROM 

THE JURASSIC ROCKS OF SOLENHOFEN - - 135 

48. Conchcscia curta, AN OSTRACOD OF THE PLANKTON, x 40 - 144 

49. Mimonectes loveni. A FEMALE SPECIMEN SEEN FROM THE 

SIDE AND FROM BELOW, SHOWING THE DISTENDED- 
BALLOON-LIKE FORM OF THE ANTERIOR PART OF THE 
BODY, x 3 - 145 

50. THE ZOEA LARVA OF A SPECIES OF Sergestes, TAKEN BY 

THE " CHALLENGER " EXPEDITION, x 25 - 146 

51. THE NAUPLIUS LARVA OF A SPECIES OF BARNACLE OF 

THE FAMILY LEPADID/E, SHOWING GREATLY-DEVELOPED 
SPINES. FROM A SPECIMEN TAKEN IN THE ATLANTIC 
OCEAN, NEAR MADEIRA, x n - - 147 

52. Calocalanus pavo, ONE OF THE FREE-SWIMMING COPEPODA 

OF THE PLANKTON. ENLARGED - 148 

53. Copilia quadrata (FEMALE), A COPEPOD OF THE FAMILY 

CORYC^ID^E, SHOWING THE PAIR OF LARGE "TELE- 
SCOPIC " EYES, x 20 - - 153 

54. Phronima colletti, MALE. FROM A SPECIMEN TAKEN IN 

DEEP WATER NEAR THE CANARY ISLANDS, x 12 - 154 

55. THE BRINE SHRIMP (Artemia salina) - 164 

56. Chydorus sph&ricus, A COMMON SPECIES OF WATER-FLEA. 

x 50 - 166 



xii THE LIFE OF CRUSTACEA 

FIG. PAGE 

57. A WATER-FLEA (Daphnia ptdex), FEMALE, WITH EPHIP- 

PIUM CONTAINING TWO "RESTING EGGS." X 2O - 167 

58. Bythotreplies longimanus, FEMALE, WITH EMBRYOS IN THE 

BROOD-SAC, x 12 169 

59. Diaptomus cceruleus, FEMALE, x 25 171 

60. Asellus aquaticus, FEMALE, x 4 - - 173 

61. MAP SHOWING THE DISTRIBUTION OF CRAYFISHES - 175 

62. A WELL SHRIMP (Niphargus aquilex). x 7 - 185 

63. THE SEA-SLATER (Ligia occanica). ABOUT TWICE NATURAL 

SIZE - 200 

64. STRUCTURE OF THE BREATHING ORGANS OF Porcellio 

scaber - - 202 

65. Armadillidium vulgar e. x 2^ - 203 

66. Two BRANCHES OF A CORAL (Seriatopora) SHOWING 

"GALLS" INHABITED BY THE CRAB Hapalocarcinus 
marsupialis. ON THE RIGHT THE FEMALE CRAB, 

EXTRACTED FROM THE GALL AND FURTHER ENLARGED 211 

67. Hyperia galba, FEMALE. ENLARGED - - 213 

68. A, THE CRAB Melia tessellata CLINGING TO A BRANCH OF 

CORAL, AND CARRYING IN EACH CLAW A LIVING SEA- 
ANEMONE ; B, ONE OF THE CLAWS FURTHER ENLARGED 

TO SHOW THE WAY IN WHICH THE ANEMONE IS HELD 2l6 

69. THE COMMON PEA CRAB (Pinnotheres pisum), FEMALE. 

NATURAL SIZE ... . 217 

70. Cirolana borealis. ABOUT TWICE NATURAL SIZE - - 219 

71. A, FRONT PART OF BODY OF A PRAWN (Spirontocaris 

polaris), FROM ABOVE, SHOWING ON THE RIGHT SIDE 
A SWELLING OF THE CARAPACE CAUSED BY THE 
PRESENCE OF THE PARASITE Bopyroides hippolytes IN 
THE GILL CHAMBER ; B, THE FEMALE PARASITE 
EXTRACTED AND FURTHER ENLARGED ; C, THE MALE 
PARASITE ON SAME SCALE AS THE FEMALE - - 222 

72. A FISH-LOUSE (Caligus rapax), FEMALE, x 5 - 225 

73. STAGES OF DEVELOPMENT OF Lerncea branchialis. F is 

SLIGHTLY, THE OTHER FIGURES GREATLY, ENLARGED - 226 

74. STAGES OF THE LIFE-HISTORY OF Hcsmocera dance, ONE 

OF THE MONSTRILLID^ - - 229 

75. FREE - SWIMMING STAGES OF Sacculina carcini. MUCH 

ENLARGED - - 232 



LIST OF ILLUSTRATIONS xiii 

FIG. PAGE 

76. EARLY STAGE OF Sacculina WITHIN THE BODY OF A 

CRAB 234 

77. ROSTRUM AND FORE PART OF CARAPACE, SEEN FROM 

ABOVE, OF (A) RED - CLAWED CRAYFISH (Astacus 
fluviatilis) AND (B) WHITE-CLAWED OR ENGLISH CRAY- 
FISH (Astacus pallipes) - - - 242 

78. THE COMMON SHRIMP (Crangon vulgaris). NATURAL SIZE 244 

79. THE NORWEGIAN DEEP-WATER PRAWN (Pandalus borcalis), 

FEMALE ... - - 246 

80. THE GRIBBLE (Limnoria lignorum). MUCH ENLARGED - 254 

81. RESTORATION OF A TRILOBITE (Triarthrus becki), SHOWING 

THE APPENDAGES. UPPER SIDE ON RIGHT, UNDER 
SIDE ON LEFT. SLIGHTLY ENLARGED - - 258 

82. Ceratiocaris papilio, ONE OF THE FOSSIL PHYLLOCARIDA - 262 

83. Pygocephalus cooperi, FROM THE COAL-MEASURES : UNDER 

SIDE OF A FEMALE SPECIMEN, SHOWING THE OVER- 
LAPPING PLATES OF THE BROOD-POUCH - 263 

84. THE TASMANIAN "MOUNTAIN SHRIMP" (Anaspides tas- 

mania), A LIVING REPRESENTATIVE OF THE SYNCARIDA. 
SLIGHTLY ENLARGED - - 264 

85. Praanaspides precursor, ONE OF THE FOSSIL SYNCARIDA, 

FROM THE COAL-MEASURES OF DERBYSHIRE. SLIGHTLY 
ENLARGED ------- 265 



FULL-PAGE PLATES 

PLATE FACING PAGE 

I. MALE AND FEMALE LOBSTERS, SHOWING THE DIFFER- 
ENCE IN THE RELATIVE BREADTH OF THE ABDOMEN 
IN THE Two SEXES. THIS FIGURE ALSO ILLUSTRATES 
THE DISSIMILARITY OF THE LARGE CLAWS, AND THE 
FACT THAT THE "CRUSHING CLAW " MAY BE ON 
EITHER THE RlGHT OR LEFT SlDE OF THE BODY. 
(From Brit. Mus. Guide) - 26 

II. Apus cancriformis FROM KIRKCUDBRIGHTSHIRE. SLIGHTLY 

ENLARGED - - - 63 



xiv THE LIFE OF CRUSTACEA 

PLATE FACING PAGE 

-GROUP OF SPECIMENS OF THE GOOSE BARNACLED 
(Lepas anatifera), ONE SHOWING THE CIRRI EX- 
TENDED AS IN LIFE. NATURAL SIZE. (From Brit. 

III. ( Mus. Guide) } 42 

GROUP OF A COMMON SPECIES OF ACORN-SHELL OR 
ROCK BARNACLE (Balanus balanoides). NATURAL 
SIZE 

IV. Penceus caramote, FROM THE MEDITERRANEAN. ABOUT 

HALF NATURAL SIZE. (From Brit. Mus. Guide) - 57 

V. THE COMMON SPINY LOBSTER (Palinurus vulgar is). 

MUCH REDUCED. (From Brit. Mus. Guide) - - 59 

VI. Munida rugosa. BRITISH. REDUCED - - 60 

VII. THE COMMON HERMIT CRAB, Eupagurus bernhardus, IN 
THE SHELL OF A WHELK. REDUCED. (From Brit. 
Mus. Guide) - - - - - -62 

VIII. THE "NORTHERN STONE CRAB," Lithodes maia. 

MUCH REDUCED. THE LAST PAIR OF LEGS ARE 
FOLDED OUT OF SlGHT IN THE GlLL CHAMBERS. 

(From Brit. Mus. Guide) 63 



'THE COMMON SHORE CRAB (Carcinus manas). RE-" 



IX.. 



DUCED 



Dromia vulgaris, CARRYING ON ITS BACK A MASS OF 
THE SPONGE, Clione celata. BRITISH. REDUCED 



'{ 



A SWIMMING CRAB, Portunus depurator. BRITISH.' 
j. i REDUCED 

] A SPIDER CRAB, Maia squinado, DRESSED IN FRAG- 
MENTS OF WEEDS. BRITISH. REDUCED 



68 



X. Calappa flammea. BRAZIL. REDUCED - - 72 

XI. THE GIANT JAPANESE CRAB, Macrocheira hampferi. 

MALE. THE SCALE OF THE FIGURE is GIVEN BY 
A TWO-FOOT RULE PLACED BELOW THE SPECI- 
MEN. (From Brit. Mus. Guide) - 76 

XII. Squilla mantis, FROM THE MEDITERRANEAN. ABOUT 

ONE-HALF NATURAL SIZE. (From Brit. Mus. Guide) 80 



LIST OF ILLUSTRATIONS 



xv 



FACING PAGE 



XIV.- 



XX. - 



THE MURRAY RIVER " LOBSTER," Astacopsis 
spinifer. NEW SOUTH WALES. MUCH REDUCED 

THE LAND CRAYFISH, Engaus cunicularis. TAS- 
MANIA. NATURAL SIZE 



XXI. Palamon jamaicensis. A LARGE FRESHWATER 
PRAWN OF THE FAMILY PAL^EMONID^. WEST 
INDIES. MUCH REDUCED - 



XXIII. . 



100 



'Corystes cassivelaunus. MALE (ON LEFT) AND FEMALE^ 

(ON RIGHT). BRITISH. REDUCED 
Albunea symnista, ONE OF THE HIPPIDEA. INDIAN j 

SEAS. REDUCED J 

(Ocypode cursor. WEST AFRICA. REDUCED "| 

XV. < Gelasimus tangeri. MALE ABOVE, FEMALE BELOW. V 104 
^ WEST AFRICA. REDUCED 

XVI. A DEEP-SEA HERMIT CRAB, Parapagurus pilosimanus, 

SHELTERED BY A COLONY OF EpiZOdnthuS. FROM 

DEEP WATER OFF THE WEST OF IRELAND. 
SLIGHTLY REDUCED ----- 124 

XVII. A DEEP - SEA PRAWN, Nematocarcinus undulatipes. 

SLIGHTLY REDUCED. (From Brit. Mus. Guide) 128 

XVIII. Bathynomus giganteus. ABOUT ONE-HALF NATURAL 
SIZE. (From Lankester's "Treatise on Zoology," 
after Milne-Edwards and Bouvier) - 131 

ILatreillia elegans, ONE OF THE DROMIACEA WHICH ^1 
RESEMBLES A SPIDER CRAB. FROM THE 
MEDITERRANEAN. NATURAL SIZE \ I 55 

THE GULF-WEED CRAB, Planes minutus. SLIGHTLY I 
ENLARGED 



177 



179 



XXII. Atya scabra. A FRESHWATER PRAWN OF THE 

FAMILY ATYID^. WEST INDIES. REDUCED - 180 



THE RIVER CRAB OF SOUTHERN EUROPE, Potamon\ 

edule (OR Telphusa fluviatilis). REDUCED 
Sesarma chiragra. A FRESHWATER CRAB OF THE > 182 

FAMILY GRAPSID*. FROM BRAZIL. SLIGHTLY I 

REDUCED 



XVI 



THE LIFE OF CRUSTACEA 



PLATE 

XXIV. 
XXV. 



XXVI. 

XXVII. 
XXVIII. 

XXIX. 
XXX. 

XXXI. 
XXXII. 



FACING PAGE 

Mglea lavis. SOUTH AMERICA. NATURAL SIZE - 184 

THE BLIND CRAYFISH OF THE MAMMOTH CAVE 
OF KENTUCKY, Cambarus pellucidus. NATURAL 
SIZE ... 



{A WEST INDIAN LAND CRAB, Gecarcinus ruricola." 
REDUCED 
A LAND HERMIT CRAB, CcenoUta rugosa. RE- 
DUCED 

THE Coco NUT CRAB, Birgus latro. MUCH RE- 
DUCED 

GROUP OF BARNACLES, Coronula diadema, ON THE 
SKIN OF A WHALE. JAPAN. REDUCED - 

(Cymothoa oestrum, AN ISOPOD PARASITE OF FISH.' 
SLIGHTLY ENLARGED 
Sacciilina carcini ATTACHED UNDER THE ABDOMEN 
OF A COMMON SHORE CRAB. REDUCED 

THE " NORWAY LOBSTER," Nephrops norvegicus. 
ABOUT ONE-THIRD NATURAL SIZE. (From Brit. 
Mus. Guide) 

THE COMMON EDIBLE CRAB, Cancer pagurus. 
BRITISH. MUCH REDUCED 

PIECE OF TIMBER FROM RYDE PIER, SHOWING 
DAMAGE CAUSED BY Limnoria AND Chelura. 
(From Brit. Mus. Guide) 



186 



>- 190 



196 



209 



240 



248 



255 




THE LIFE OF CRUSTACEA 




THE LIFE OF CRUSTA 



CHAPTER I 

INTRODUCTORY 

TTVERYONE has some acquaintance with the 
JL-rf animals that are grouped by naturalists under 
the name Crustacea. The edible Crabs, Lobsters, 
Prawns, and Shrimps, are at least superficially 
familiar, either as brought to the table or as 
displayed in the fishmonger's, and the most un- 
observant of seaside visitors must have had his 
attention attracted by living specimens of some of 
the more obtrusive species, such as the common 
Shore Crab. Many, however, will be surprised to 
learn that the Barnacles coating the rocks on the 
seashore, the Sand-hoppers of the beach, and the 
Woodlice of our gardens, are members of the same 
class. Still less is it suspected, by those who have 
not given special attention to the subject, that the 
living species of the group number many thousands, 
presenting strange diversities of structure and habits, 
and playing important parts in the general economy 
of Nature. 



2 THE LIFE OF CRUSTACEA 

In addition to those just mentioned, a few Crus- 
tacea are sufficiently well known to be distinguished 
by popular names, such, for example, as Crayfish 
and Hermit Crabs, but for the vast majority no 
names are available except those of technical 
zoology. In the following pages, therefore, while 
technical terms have been introduced as sparingly 
as possible, the unfamiliarity of the animals them- 
selves makes it needful to use many unfamiliar 
names. 

In the classification of the Animal Kingdom, the 
Crustacea form one of the divisions of a compre- 
hensive group, or Phylum, known as Arthropoda. 
The typical members of this group have a more or 
less firm external skeleton, the body is divided into 
segments, there are jointed limbs, and some of these 
are modified to serve as jaws. The chief divisions 
or classes of the Arthropoda are (i.) Insecta, in- 
cluding Butterflies, Moths, Bees, Wasps, Flies, 
Beetles, and the like ; (ii.) Chilopoda, or Centipedes ; 
(iii.) Diplopoda, or Millipedes 1 ; (iv.) Onychophora, in- 
cluding the curious worm-like Peripatus ; (v.) Arach- 
nida, or Scorpions, Spiders, Mites, and their allies ; 
and (vi.) Crustacea. 

It is not easy to summarize in a few words the 
characters common to all Crustacea, and distinguish- 
ing them from the other groups of Arthropoda. As 

1 The Chilopoda and Diplopoda are sometimes regarded as 
forming a single class Myriopoda. 



INTRODUCTORY 3 

a rough guide to classification, it is useful to remember 
that an Insect "can generally be recognized by having 
three pairs of walking legs, an Arachnid by having 
four pairs, and a Centipede or Millipede by having a 
great many pairs, all nearly alike. The Crustacea, 
on the other hand, show great diversity in the number 
and arrangement of their walking or swimming legs, 
but they rarely show any special resemblance to those 
of the other large groups of Arthropoda. Thus, for 
example, a common species of Woodlouse, Armadil- 
lidium vulgare, is very similar at first sight to the 
Millipede Glomeris marginata, but it has only seven 
pairs of walking legs, while the Millipede has seven- 
teen or nineteen pairs. 

More precisely, it may be said of the great majority 
of Crustacea that they are aquatic animals, breathing 
by gills or by the general surface of the body, having 
two pairs of " feelers," or antennae, on the front part 
of the head, and at least three pairs of jaws. Excep- 
tions to each of these statements will be mentioned 
in later chapters in dealing with parasites and other 
highly modified types. In such cases, however, the 
larval or young stages afford indications of affinity, 
and comparison with less modified forms enables us 
to trace a connection with the typical Crustacea. 

The best way to form a conception of a group ol 
animals, however, is not to attempt in the first place 
to define its limits, but to begin by studying the 
structure of some typical and central species, and 



4 THE LIFE OF CRUSTACEA 

afterwards to note the divergences from this type 
presented by other members of the group. Speaking 
very generally, it may be said that these divergences 
are of two kinds. On the one hand there are char- 
acters that have no apparent relation to the animal's 
habits and mode of life, and on the other hand there 
are modifications of structure which are more or less 
plainly of use to the animal. It is to characters of 
the former class that we look for evidence of an 
animal's affinities, and it is upon them that our 
systems of classification are chiefly based. The 
characters of the second class " adaptive " char- 
acters, as they are called become of importance 
when we study the animal "as a going concern," 
so to speak, and endeavour to understand how its 
life is carried on in relation to its surroundings. 

In pursuance of this plan of study, the next chapter 
will be devoted to a description of the Common 
Lobster as a type of the Crustacea. In the third 
chapter a survey of the classification of the group 
will be given ; since, however, the characters on 
which the classification is based cannot be explained 
fully without entering into technical details which 
are beyond the scope of this work, this survey will 
be restricted to what is necessary for comprehension 
of the succeeding chapters. In the fourth chapter 
some account is given of the young or larval stages 
of Crustacea, and of the changes they undergo in the 
course of development. 



INTRODUCTORY 5 

In the next five chapters the Crustacea are classified 
according to their habitats, and those living in the 
shallow waters, the depths, and the surface of the 
ocean, in the fresh waters, and on land, are discussed 
in turn ; while a separate chapter is devoted to the 
curious forms that live as parasites on, or as associates 
with, other animals. The last two chapters deal 
respectively with the Crustacea as they affect man, 
and with the past history of the group as revealed 
by fossil remains. 



CHAPTER II 
THE LOBSTER AS A TYPE OF CRUSTACEA 

THE most noticeable feature distinguishing the 
Lobster 1 (Fig. i) at first sight from other 
familiar animals is the jointed shelly armour that 
encases its body and limbs. Over the fore part of 
the body this armour is continuous, forming a shield, 
or carapace, which projects in front, between the 
eyes, as a toothed beak, or rostrum ; on the hinder 
part the tail, or abdomen it is divided into six 
segments, or somites, connected with each other by 
movable joints. Each of these somites carries on 
the under-side a pair of fin-like limbs, or swimmerets, 
the last pair of which (uropods) are much larger than 
the others, and are spread out at the sides of a middle 
tail-plate, or telson, forming what is known as the 
tail-fan. Since the fore part of the body also has a 
series of paired limbs, constructed, as will be shown 

1 The account given here of the structure of the Lobster 
applies almost equally well to the River Crayfish or the Norway 
Lobster. The student is recommended to follow the description 
with a specimen of one of these animals before him. 

6 



THE LOBSTER AS A TYPE OF CRUSTACEA 7 



later, on the same plan as the swimmerets, it is 
concluded that this part also is built up of somites, 
which have become soldered together. That this 
conclusion is correct is shown by comparison with 
some of the lower Crustacea in which this part of 
the body is divided up into eight separate somites, 
like those of the abdomen, each carrying, in place of 



Abdomen. 
Somites 



Cerihalothorajc 

Caranace . y * 

Rostrum 



Antennule 



nna 




Walking legs 

FIG. i THE COMMON LOBSTER (Homarus gammarus), FEMALE, 
FROM THE SIDE. (From British Museum Guide.) 

the swimmerets, a pair of walking legs. In front of 
these eight somites, forming what is called the thorax, 
is the head a part of the body which is never, in 
any Crustacean, broken up into distinct somites, but 
which, since it carries five pairs of appendages, must 
consist of at least five somites. The part of the 
body covered by the Lobster's carapace includes 
both the head and the thorax, and is known, there- 



8 THE LIFE OF CRUSTACEA 

fore, as the cephalothorax. It is necessary to bear in 
mind that the parts of the body to which the names 
head, thorax, and abdomen, are applied in Crustacea 
are by no means exactly equivalent to those which 
bear the same names in Insects, for example, and 
that, beyond a rough similarity in position, they 
have no sort of relation to the parts so named in the 
body of a vertebrate animal. 

There are altogether twenty pairs of appendages 
attached to the body of the Lobster. In front of the 
head are the stalked eyes (of which the nature will be 
discussed later) and two pairs of feelers the anten- 
nules and antenna (sometimes called the first and 
second antennae). Near the mouth on the under- 
side of the head are three pairs of jaw-appendages 
the strong mandibles and the flattened, leaf-like 
maxilhdce and maxilla. Following these are the 
appendages of the thorax, of which the first three 
are intermediate in form between the true jaws and 
the legs, and are therefore termed foot-jaws, or 
maxillipeds. The remaining five pairs of thoracic 
limbs are the legs, the first pair forming the large 
and powerful pincer-claws, or chelipeds, while the 
others are the walking legs. The six pairs of 
swimmerets on the abdomen have already been 
mentioned. 

If one of the somites of the abdomen be separated 
from the others, it will be seen (Fig. 2) to consist of 
a shelly ring, to which the two swimmerets are 



THE LOBSTER AS A TYPE OF CRUSTACEA 9 



Tergum 




attached, wide apart, on the under-side. The arched 
upper part of the ring is known as the tergum, and 
the more flattened under-part as the sternum. On 
each side the tergum overlaps the sternum, and 
hangs down as a side-flap, or pleuron. On the 
upper side of the abdomen 
the terga of the somites 
overlap, the front part of 
each being pushed under 
the tergum in front when 
the abdomen is straight- 
ened, and only exposed to 
view when the abdomen is 
bent. Below, the sternum 
of each somite is seen to 
be only a narrow bar, con- 
nected with those in front 
and behind by soft mem- 
brane, and there is no over- 
lapping. At the sides the somites are connected 
together by hinge-joints, which allow them to move 
only in a vertical plane. Thus the abdomen can be 
straightened out or bent downwards and forwards, 
but cannot be moved from side to side. In life the 
Lobster can swim backwards through the water by 
vigorously flapping the abdomen. 

The carapace which covers the upper side of the 
head and thorax is not formed, as might be thought, 
simply by the terga of the somites becoming soldered 



Pleuron 



Appendage 



FIG. 2 ONE OF THE AB- 
DOMINAL SOMITES OF THE 
LOBSTER, WITH ITS APPEN- 
DAGES, SEPARATED AND 
VIEWED FROM IN FRONT. 

(From British Museum 
Guide.) 



io THE LIFE OF CRUSTACEA 

together. This is shown by a comparison with 
certain shrimp-like Crustacea (Mysidacea) in which 
the carapace arises, like a fold of the skin, from the 
hinder edge of the head, and envelops, like a loose 
jacket, the distinctly segmented thorax. In the 
Lobster this fold has become adherent to the 
thoracic somites down the middle of the back, but 
at the sides it hangs free, enclosing on each side 
a cavity within which lie the gills. 

It seems at first sight strange to include in the 
same category as " limbs " or " appendages " organs 
which differ so much in form and function as do 
the swimmerets, the walking legs, the jaws, and the 
antennae. Nevertheless it can easily be demon- 
strated that all of them are constructed on the same 
general plan, and arise in the embryo from rudiments 
which are, for the most part, exactly alike. This is 
expressed in technical language by saying that the 
appendages of the whole series are homologous with 
one another. A full discussion of this interesting 
fact would require more space than can be devoted 
to it here, but a few examples may be given to illus- 
trate what is meant by the " serial homology " of 
the appendages in Crustacea. 

If one of the swimmerets be detached from the 
third abdominal somite, it will be seen (Fig. 2) to 
consist of a stalk, known as the protopodite, bearing 
two branches, of which that on the outer side is 
called the exopodite, and that on the inner side the 



THE LOBSTER AS A TYPE OF CRUSTACEA n 

endopodite. The protopodite consists of two seg- 
ments, the first very short, and the second much 
longer. It can easily be seen that the side-plates of 
the tail-fan (the middle plate, as already mentioned, 
is the telson) are simply the swimmerets of the sixth 
abdominal somite. They are much larger than the 
other swimmerets, and have the endopodite and 
exopodite broadened 
out into large plates ; 
while the protopodite x 4.-.,, -. 

\ 4 f.-:< tf Exopodite 

is very short, and not 




divided into segments. Mt ;; )^ J CLU 

If now the third max- 

ProtOfiodite 

ilhped (Fig. 3) be ex- 
amined, it Will be found FlG . 3 _ T HiRD MAXILLIPED OF 

that, like the swim- LOBSTER (From British Mu- 

seum Guide.) 

meret, it consists essen- 
tially of two branches springing from a stalk of 
two segments. The exopodite, however, is much 
smaller than the endopodite, and it ends in a flexible 
lash made up of many small segments. The endo- 
podite forms the main part of the limb, and has 
five segments, so that, with the two segments of the 
protopodite, there are seven segments in the main 
axis of the limb ; the second and third segments 
are partly soldered together, but the line of union 
can be plainly seen. Attached to the outer side of 
the first segment is a membranous plate, known as 
the epipodite, on which is inserted, near its base, a 



12 



THE LIFE OF CRUSTACEA 



brush-like structure, which is one of the gills. In 
the natural position the epipodite and its gill lie in 
the gill chamber, hidden from view by the side-flap 
of the carapace. 

The legs (Fig. 4) can, without difficulty, be seen 
to consist each of seven segments like those of the 

maxillipeds, but there 
is no exopodite. In the 
young Lobster, when 
just hatched from the 
egg, however, each of 
the legs has a large 
exopodite like that of 
the third maxilliped. 
These exopodites, which 
are used in swimming, 
are afterwards lost as 
the animal grows ; but 

A, of first pair ; B, of third pair their presence in the 

young is interesting as 

confirming the conclusion that the legs, like the 
maxillipeds, are built on the same plan as the swim- 
merets. The large claws, and also the first and 
second pairs of walking legs, end in pincers, or chela, 
the penultimate segment projecting in a thumb-like 
process against which the last segment works. Each 
leg, except those of the last pair, has on its first 
segment an exopodite with a gill like those of the 
maxilliped. 





FIG. 



4 WALKING 
LOBSTER 



LEGS OF 



THE LOBSTER AS A TYPE OF CRUSTACEA 13 

Following the series of appendages forwards from 
the third maxilliped (Fig. 5), it is easy to trace the 
gradual reduction of the endopodite and exopodite ; 





-ex 







,sc 



-ex 




FIG. 5 APPENDAGES OF LOBSTER IN FRONT OF THIRD MAXILLIPED 

A, Eye-stalk ; B, antennule ; C, antenna (the flagellum is cut short) ; 
D, mandible; E, maxillula ; F, maxilla; G, first maxilliped ; H, 
second maxilliped. en, Endopodite ; ep, epipodite ; ex, exopodite ; 
gn, gnathbbases, or jaw-plates; p, palp of mandible; sc, scapho- 
gnathite 



14 THE LIFE OF CRUSTACEA 

while the two segments of the protopodite become 
flattened and broadened inwards to form the jaw- 
plates. The mandibles (Fig. 5, D), which are the 
chief organs of mastication, consist mainly of the 
much enlarged basal segment of the protopodite, 
with a strongly toothed inner edge, where it works 
against its fellow of the opposite side ; and the rest 
of the limb is reduced to a small sensory " palp," 
which represents the second segment of the protopo- 
dite and the endopodite. 

The antennae (Fig 5, C) can be shown, without 
difficulty, to conform to the same plan of structure 
as the other appendages. The two segments of the 
protopodite are short, but distinct ; the endopodite 
forms the long lash, or flagellum, composed of very 
numerous small segments ; the exopodite is reduced 
to a small movable scale or spine. 

The antennules (Fig 5, B) seem at first sight to 
present the two-branched type of structure in its 
simplest form ; but there is considerable doubt as to 
whether the two lashes which each bears on a three- 
segmented stalk are really equivalent to the endopo- 
dite and exopodite. 

The movable stalks which carry the eyes (Fig. 5, A) 
have been considered by some to belong to the series 
of the appendages, and to be, in fact, modified limbs. 
If this be the case, we have here the greatest simpli- 
fication which the limb undergoes in the Lobster, for 
each eye-stalk consists only of two segments : the 



THE LOBSTER AS A TYPE OF CRUSTACEA 15 

first small and incompletely formed, the second in 
the form of a short cylinder, having the eye at 
its end. There are, however, reasons for doubting 
whether the eye-stalks are really appendages. 

The hard outer covering of the Lobster not only 
protects and gives support to the internal organs, 
but also affords points of attachment for the muscles 
by means of which the animal moves. In other 
words, it plays the part of a skeleton ; but since, 
unlike the skeleton of vertebrate animals, it is outside 
instead of inside the soft parts of the body, it is 
known as an exoskeleton. Closer examination shows 
that this outer covering is really continuous over the 
whole of the body and limbs, but is thin and soft 
at the joints, allowing the parts to move one upon 
another. It is composed of a horn-like substance 
known as chitin, which, except at the joints, is 
hardened by the deposition in it of carbonate and 
other salts of lime. 

As this external covering does not increase in size 
after it has been formed, and as it cannot stretch to 
any great extent, the Lobster requires to cast its 
shell at intervals as it grows. In this process of 
moulting the integument of the back splits between 
the carapace and the first abdominal somite. The 
body and limbs are gradually worked loose and 
withdrawn through the opening, leaving the cast 
shell with all its appendages almost entire. The 
new covering, which had been formed underneath the 



i6 



THE LIFE OF CRUSTACEA 



old before moulting, is at first quite soft, and the 
animal rapidly increases in size owing to the absorp- 
tion of water. The shell then gradually hardens by 
the deposition of lime salts. 

The internal anatomy (Fig. 6) presents many points 
of interest which can only be briefly touched on here. 
The food-canal consists of a short gullet leading into 
a capacious stomach, from which the straight in- 



Ofiening of Hirer- cf act- 
Optic Nerve 

\Brqin If^ 

^ Stomach. * \ 



Superior atraominZd artery 
Intestine 




FIG. 6 DISSECTION OF MALE LOBSTER, FROM THE SIDE. (From 
British Museum Guide.) 

testine runs to the vent on the under-side of the 
telson. The stomach has a most remarkable and 
complicated structure. It consists of two chambers, 
a larger in front and a smaller behind, which are 
lined by a continuation of the chitinous outside 
covering of the body. This chitinous lining is 
thickened in places to form a system of plates and 
levers connected with three strong teeth set in the 
nawow opening between the two chambers. By the 



THE LOBSTER AS A TYPE OF CRUSTACEA 17 

action of muscles attached to certain of these plates 
the teeth work together so as to divide up the food 
more finely than had been done by the mandibles 
and other jaws. The whole apparatus, in fact, serves 
as a kind of gizzard, and is known as the gastric 
mill. 

A small part of the intestine at the hinder end is 
lined, like the stomach, by a continuation of the 
chitinous covering, which is turned in at the vent. 
This lining and that of the stomach, with the plates 
and teeth of the gastric mill, are cast and renewed 
when the shell is moulted. 

On each side of the food-canal in the thorax lies a 
.large mass of soft tissue, yellowish-green in colour. 
This is the digestive gland, or " liver," which secretes 
the digestive juice, discharging it into the food- 
canal by a short duct on each side just behind the 
stomach. 

The heart lies in the middle of the back, just under 
the hinder part of the carapace, and gives off, in 
front and behind, a number of arteries which carry 
the blood to the various organs of the body. From 
the smaller branches of these arteries the blood 
passes, not, as in vertebrate animals, into capillaries, 
but into the spaces lying between the organs of the 
body, and it finds its way back to the heart, not in 
definite veins, but by ill-defined venous channels 
which open into the pericardium, or space surround- 
ing the heart. From the pericardium the blo<*l 



i8 



THE LIFE OF CRUSTACEA 



enters the heart by six openings in its walls, each 
guarded by a pair of valves which close when the 
heart contracts, and prevent the blood from returning 
to the pericardium. 

The venous channels which convey the blood 
back to the heart are so arranged that most of the 




FIG. 7 GILLS OF THE LOBSTER, EXPOSED BY CUTTING AWAY THE 
SIDE-FLAP OF THE CARAPACE (BRANCHIOSTEGITE) 



blood passes first through the gills, for the purpose 
of respiration, before it reaches the heart and is 
again distributed through the body. These gills, 
as already mentioned, lie in the two branchial 
chambers under the side-flaps of the carapace 
(Fig. 7), and are attached, some to the epipodites 
of the thoracic limbs (as described above), and 
some to the soft membrane of the joints between 
the limbs and the body ; while others are attached 



THE LOBSTER AS A TYPE OF CRUSTACEA 19 

to the side-wall of the thorax itself. Each gill is 
somewhat like a bottle-brush in shape, consisting 
of a central stalk set round with rows of soft hair- 
like processes. As the blood streams through the 
minute channels inside these filaments, it is separated 
only by a thin membrane from the surrounding 
water, and the absorption of oxygen and discharge 
of carbon dioxide can go on easily. For this purpose, 
however, it is necessary that the water within the 
gill chamber should be constantly renewed, and this 
is effected in the following way : the front part of 
the gill chamber forms a narrow channel running 
forward under the side - wall of the carapace. 
Within this channel lies a large plate known as the 
scaphognathite, attached to the outer side of the 
maxilla, which during life is constantly in move- 
ment, causing a current of water to flow forwards 
through the channel. The water enters the gill 
chamber by the narrow slit-like space between the 
lower edge of the carapace and the bases of the 
legs, and is discharged in front at the sides of the 
head, where its movement is helped by the vibrating 
exopodites of the maxillipeds. 

At the sides of the stomach, in the front part of 
the head, lie a pair of glands which, from their 
colour, are known as the green glands. These are 
the excretory organs, corresponding in function to 
the kidneys of the higher animals. Each has con- 
nected with it a thin-walled bladder, which opens to 



20 THE LIFE OF CRUSTACEA 

the outside through a small perforation on the 
under-side of the first segment of the antenna. 

The chief part of the nervous system is the ventral 
nerve-chain, which runs along the under-side of the 
body. This is a long cord having at intervals a 
series of knots or swellings, the ganglia or nerve- 
centres, from which nerves are given off to the 
appendages and to the organs of the body. In the 
hinder part of the thorax and in the abdomen there 
is a ganglion in each somite, but in front these 
ganglia become crowded together and coalesced, so 
that we find only a single large ganglion, correspond- 
ing to the somites from that of the mandibles to 
that of the third maxillipeds. Between the ganglia 
the cord is really double, although for the greater 
part of its length the two parts are more or less 
completely fused into one. In front of the head and 
above the gullet is a ganglion which sends nerves to 
the eyes, antenntiles and antennae, and is known as 
the brain, although it is, perhaps, hardly so important 
as that name would suggest. It is connected with 
the ventral chain by two cords that pass on either 
side of the gullet. 

The eyes, as already mentioned, are set on movable 
stalks, so that they can be turned in any direction at 
the will of the animal, and are of the type known as 
" compound eyes." If the convex black area at the 
end of the eye-stalk be examined with a strong lens, 
it will be seen that the membrane which covers it is 



THE LOBSTER AS A TYPE OF CRUSTACEA 21 

divided up into a beautifully regular series of square 
facets. This membrane is a thin and transparent 
Continuation of the chitinous covering of the body, 
and if it be stripped off and examined under a micro- 
scope, it will be found that each facet is capable of 
acting as a lens and forming an image of external 
objects. It is not to be supposed, however, that the 
Lobster sees a separate image in each of the facets, 
some thirteen thousand in number, which go to 
make up each eye. In the interior of the eye, at 
some distance from the surface, are a large number 
of rod-like bodies, connected with the fibres of the 
optic nerve, and believed to be the actual organs for 
the perception of light. Each rod corresponds to 
one of the facets, and as it lies at the bottom of a 
long conical tube, of which the walls are covered 
with dark pigment, it can only receive light from a 
single point in line with the axis of the tube. In 
this way the image of any object will be built up, 
like a mosaic, out of the impressions of light and 
darkness received through the separate facets, and 
transmitted to the underlying rods. It has been 
shown in some Crustacea that, when the animal is 
in a very dim light, the curtain of pigment separating 
the tubes is partially withdrawn, so that the light 
from each facet can reach, not one, but several rods. 
In this way the images of objects received are much 
brighter, although they are less sharply defined. 
It might be thought that in animals like the 



22 THE LIFE OF CRUSTACEA 

Lobster, enclosed in a hard shelly covering, the sense 
of touch must be very dull, if not altogether absent. 
This, however, is not the case. What is probably a 
very delicate tactile sense is provided for by the 
numerous hairs which are found, of many sorts and 
sizes, all over the body and limbs. Each of these 
hairs is really a hollow outgrowth of the chitinous 
covering, containing a delicate prolongation of the 
soft tissues underneath, and also supplied, in many 
if not in all cases, with a nerve-fibre, so that the 
slightest movement of the hair caused by contact 
with a solid body is perceived by the animal. Many 
of these hairs are themselves beset with delicate 
secondary hairs, arranged so that the whole looks 
like a feather or like a bottle-brush. These hairs 
are adapted for detecting slight movements or vibra- 
tions in the surrounding water. 

Whether Crustacea living in water can hear, in 
the sense in which the word is used of animals 
living in air, is doubtful ; but it is certain that they 
are extremely sensitive to vibrations only a little 
coarser, so to speak, than those we know as sound. 
The Lobster, and many other Crustacea, do indeed 
possess a structure which was long supposed to be 
an organ of hearing, and may possibly in part fulfil 
that function, although it is now known that that is 
not its only or even its chief use. It consists of a 
small cavity in the basal segment of the stalk of the 
antennule, opening to the outside by a narrow slit 



THE LOBSTER AS A TYPE OF CRUSTACEA 23 

on the upper surface of the segment. The cavity is 
lined by a delicate continuation of the chitinous 
covering of the body, and has on its inner surface a 
series of feathered hairs of the kind described above, 
which are richly supplied with nerve-fibres from a 
large nerve entering the base of the antennule. 
Within the cavity, and for the most part entangled 
among these hairs, are a number of grains of sand. 
When the Lobster moults, the lining membrane of 
this cavity is thrown off like the rest of the exo- 
skeleton, and with it the contained sand-grains. 
While the shell is still soft after moulting, and the 
lips of the slit are not rigid, as they afterwards 
become, fresh sand-grains find their way into the 
cavity to take the place of those which have been 
cast off. Perhaps, like some other Crustacea, the 
Lobster buries its head in the sand to insure that 
some grains may find their way in ; for its pincers 
are too clumsy for it to pick up sand-grains and to 
place them in the cavity, as some Prawns have been 
seen to do. At all events, if a freshly moulted 
Prawn be placed in a vessel of sea-water, and 
supplied, instead of sand, with powdered glass or 
metal filings, particles of glass or metal will after a 
short time be found in its antennular cavities. This 
habit has been utilized in a very ingenious experi- 
ment by which the function of these organs was 
demonstrated. A Prawn had been induced in this 
way to place particles of iron filings in the cavities, 



24 THE LIFE OF CRUSTACEA 

and a strong electro-magnet was brought near the 
side of the vessel in which it was kept. It was 
observed that the Prawn, which had been swimming 
in the usual horizontal position, at once turned the 
under-side of its body towards the magnet, and swam 
about on its side as long as the magnet was in 
action. When the current exciting the magnet was 
cut off, the animal resumed its ordinary position. 
This experiment shows that these organs, to which 
we may now give their proper name of staiocysts, 
are organs for perceiving the direction of the force 
of gravity. The magnetic force acted on the 
particles of iron in the same way that the force of 
gravity acts on the sand-grains in normal conditions, 
and the Prawn felt the weight of them, so to speak, 
pulling towards the side instead of the bottom ot 
the vessel, and turned its body accordingly, to swim, 
as it supposed, right side up. It is now known that 
those parts of the human ear called the " semi- 
circular canals " have a somewhat similar function 
as " organs of orientation," although to animals 
walking on the solid ground this function is not so 
important as it doubtless is to animals swimming in 
water. 

The sense of smell is believed to have its seat 
chiefly in the antennules. The outer branch of each 
antennule bears tufts of peculiar hairs, in which the 
chitinous covering is extremely delicate, so that sub- 
stances dissolved in the water can easily pass through 



THE LOBSTER AS A TYPE OF CRUSTACEA 25 

and affect the nerve-endings within. These hairs are 
known as " olfactory filaments." 

The sense of taste in aquatic animals is, perhaps, 
not sharply defined from that of smell, but it is 
not very rash to assume that certain hairs on the 
mouth parts and on the fleshy upper and lower lips 
which bound the opening of the mouth have to do 
specially with this sense. 

The relative importance of the various senses in 
the Lobster is well illustrated in the following account 
of its habits given by Dr. H. C. Williamson in the 
Report of the Scottish Fishery Board for 1904. 
After noticing that, in daylight at least, the Lobster 
appears to be " purblind," only distinguishing light 
from shadow, Dr. Williamson goes on : " It tests 
a shadow with its antennae, or sometimes, when a 
strong shadow is thrown on it, it jumps at it with 
its chelae outstretched and snapping. It is dependent 
on its antennae for guiding it in safe places. It 
is especially careful in testing any hole before it is 
satisfied with it. It discovers the cavity by means 
of its antenna, which is waved well out to the side 
and in front as it walks. It searches the innermost 
depths of the hole with the antenna, and then inserts 
its chela. If the examination with the chela is also 
satisfactory, it immediately turns and backs smartly 
into the hole. In feeding it is guided to the food by 
the antennules. A piece of food which is dropped 
near a Lobster may fall quite unnoticed unless it 



26 THE LIFE OF CRUSTACEA 

happens to touch the antenna or the [legs]. It is 
not seen at all. But sooner or later, according as 
the distance is short or great, the scent of the food, 
carried by the currents set up by the exopodites of 
the maxillipeds, reaches the Lobster. The Lobster 
is immediately excited, although previously it was 
lying quite inert in its hole. It whips the water 
with its antennules in a staccato fashion, and feels 
about with the antennae and chelae, at first without 
leaving its hole. At once both antennules are seen 
to be whipping in the direction in which the food 
is lying, and an active search is made with the 
antennas. If they do not succeed in locating the 
bait, the lobster rather reluctantly leaves its hole, 
but cautiously, feeling all round about with its 
antennae. It goes off straight in the direction in 
which the food is lying, and, if it misses it with its 
antennas and chelae, walks over it and gets it with 
its chelate [walking legs] ; it usually picks up its 
food with the second [walking leg]. Meanwhile 
the expected feast has by association stimulated the 
maxillipeds, which are actively working as if they 
were already masticating the food. Once the food 
is seized it is conveyed to the maxillipeds, and the 
Lobster retreats to its hole, there to enjoy its meal." 
Lobsters, like most other Crustacea, are of separate 
sexes. The females (see Plate I.) may be distin- 
guished from the males by the fact that the abdomen 
is broader and has deeper side-plates, and by differ- 



PLATE I 




a a a 

i- 2 ~ 



xg 3 



a * 
S ~ a 



THE LOBSTER AS A TYPE OF CRUSTACEA 27 

ences in the form of the first two pairs of swimmerets. 
In the female the first pair, which have only one 
branch, are short and slender filaments, while in 
the male they are stout and peculiarly twisted rods. 
The second pair in the female are similar in form to 
the succeeding pairs, but in the male they have an 
additional lobe on the inner branch. The openings 
of the generative organs will be found in the male 
on the basal segments of the last pair of legs, while 
in the female they occupy the same position on the 
legs of the last pair but two. The testis of the male 
lies in the thorax, just below the heart. The ovary, 
which has the same position in the female, is usually 
much more conspicuous, and from its red colour in 
the cooked lobster it is known as the " coral." On 
the under-side of the thorax of the female, between 
the last two pairs of legs, is a three-lobed structure 
enclosing a cavity known as the "sperm-receptacle." 
Its function is to receive the fertilizing substance 
from the male, and to retain it until the eggs are 
ready to be deposited. 

In the Lobster, as in many other Crustacea, the 
eggs are carried by the female until they hatch. 
After being extruded from the oviducts, they are 
attached by a kind of cementing substance to the 
swimmerets, where they hang in bunches. The 
swimmerets are kept constantly moving, so that the 
eggs may obtain the oxygen necessary for the de- 
veloping embryos within. A female Lobster carrying 




28 THE LIFE OF CRUSTACEA 

eggs in this way is said by the fishermen to be " in 
berry," and may carry, according to its size, from 
about 3,000 to nearly 100,000 eggs. A period of 
about ten months elapses between the deposition 
of the eggs and hatching. 

The young Lobster when first hatched (Fig. 8) 
differs considerably in general appearance from the 

adult animal. The 
abdominal somites 
have a row of spines 
down the middle of 
the back, and the 

FIG. 8 FIRST LARVAL STAGE OF telson has a forked 
THE COMMON LOBSTER, x 4. cV, ane There are nn 
(After Sars.) na P e< * nere are E 

swimmerets, but, as 

already mentioned, the legs bear large exopodites, 
which are used like oars, and by means of these 
the larval Lobster swims about at the surface of the 
sea. The claws or chelae are at first hardly larger 
than the other legs, but later they increase in size, 
the swimmerets are developed, the exopodites of 
the legs are lost, and the young Lobster, sinking to 
the bottom of the sea, takes on the creeping habits 
and gradually assumes the shape of the adult. 

In many Crustacea the changes of shape or meta- 
morphoses undergone after hatching are much 
greater than in the Lobster. Some of these changes 
and their probable significance will be considered at 
greater length in a later chapter. 



THE LOBSTER AS A TYPE OF CRUSTACEA 29 

The two large claws of the Lobster (see Plate I.) 
are not quite alike in size or in shape. The smaller 
of the two has the inner edges of the fingers sharp 
and set with saw-like teeth ; the larger has the 
fingers armed with blunt rounded knobs. The 
larger claw is adapted for crushing the shells of the 
animals on which the Lobster feeds, while the smaller 
serves for holding and tearing the prey. In the 
Lobster, as in many of the higher Crustacea in which 
this asymmetry occurs, the larger claw may be 
indifferently on either side of the body. There are 
certain cases, however, among Crabs where the large 
claw is constantly on the same side of the body, or, 
in other words, all the individuals are either right- 
handed or, more rarely, left-handed. 

If a Lobster be caught by one of its claws or by a 
leg, it very readily parts with the limb in its struggles 
to escape ; and if one of the limbs be crushed or 
otherwise injured, it is often cast off by the animal. 
The separation always takes place at the same point, 
near the base of the limb, and is not simply due to 
the limb breaking at its weakest part. It is a reflex 
act, brought about by a spasmodic contraction of 
some of the leg muscles. At the place of separation, 
corresponding to the junction of the second and 
third segments of the limb, which, as already men- 
tioned, are soldered together, the internal cavity is 
crossed by a transverse partition, having only a small 
aperture in the centre through which the nerves and 



3 o THE LIFE OF CRUSTACEA 

bloodvessels pass. When the limb is cast off, this 
small opening quickly becomes closed by a clot of 
blood, and further bleeding is stopped. If, as some- 
times happens, a limb which has been seriously 
injured is not cast off, the animal not infrequently 
bleeds to death. This power of self-mutilation or 
autotomy, as it is called, is frequently used by Crus- 
tacea as a means of escaping from their enemies, 
and is closely connected with the power of regenera- 
tion of lost appendages. Beneath the scar which 
forms on the stump of a separated limb a sort of 
bud grows, and gradually assumes the form of the 
lost segments. At the next moult this straightens 
out, and, increasing in size at succeeding moults, it 
ultimately provides, in normal cases, a new member 
similar in every detail to that which had been lost. 
Occasionally it happens, under circumstances not 
yet altogether understood, that the process of re- 
generation may, so to speak, go wrong, and in this 
way various malformations and abnormalities result. 
For instance, it has been found that, if the larger, 
crushing claw of a very young Lobster be removed 
by operation or by accident, the limb which grows 
in its place may assume the form of the smaller, 
toothed claw. Further, in some other Crustacea 
(but not in the Lobster, except in the very youngest 
stages), it is found in such cases that, after removal 
of the large claw, the claw of the other side assumes 
at the next moult the form of a crushing claw, so 
that there is a " reversal of asymmetry." 



THE LOBSTER AS A TYPE OF CRUSTACEA 31 

A still more remarkable change sometimes occurs 
when one of the eye-stalks is injured. If only the tip 
of the eye-stalk be cut off, so that the nerve-ganglion 
which lies in the basal part of the stalk remains 
uninjured, it will be found that a normal eye is in 
course of time regenerated. If, however, the whole 
eye-stalk be amputated, and with it the optic ganglion, 
there grows in its place, not a new eye-stalk, but a 
segmented appendage similar to one of the flagella of 
the antennules. This fact is considered by some 
zoologists to indicate that the eye-stalks are, like the 
antennules, true appendages, homologous with the 
mouth parts and limbs, but this is a much-disputed 
question into which we cannot enter further here. 

Lobsters vary a good deal in colour, but as a rule 
a living Lobster is of a more or less mottled dark blue* 
becoming nearly black on the back, and shaded off 
into orange yellow or red on the under-side. This 
coloration resides in the shell, and does not change 
much after the shell has hardened. In this respect 
the Lobster is unlike many of the smaller Crustacea 
which have a thin and more or less transparent 
exoskeleton, and in which the colour resides in certain 
living cells (chromatophores) of the underlying 
skin. Many of these Crustacea possess the power 
of changing their colours to a remarkable degree, 
by the expansion and contraction of the branched 
chromatophores. 

The question which is often asked, " Why does a 



32 THE LIFE OF CRUSTACEA 

Lobster turn red when it is boiled ?" is one to which 
it is not easy to give a simple answer. A chemical 
change takes place under the influence of heat in the 
pigment of the shell, which changes it from blue to 
red ; how slight the change is, is perhaps shown by 
the fact that occasionally living Lobsters are found of 

a red colour almost as brilliant 

as that which is assumed on 

boiling. 
The Common Lobster is found 

on the coasts of Western 

FIG. 9-SiDE-viEw OF Europe, from Norway to the 
ROSTRUM OF (A) * 

COMMON LOBSTER Mediterranean, living in shallow 

(Homarns gammarus) .. . 

AND (B) AMERICAN water, generally a little way 




below low ' tid e mark, wherever 
a rough, rocky bottom affords 

suitable lurking-places. On the Atlantic coast of 
North America, Lobsters are also found abundantly 
in similar situations. These American Lobsters, if 
examined carefully, will be found to differ from the 
European kind in certain small details of structure. 
of which the most conspicuous is the presence, on the 
under-side of the rostrum, of two spines or teeth. In 
the European Lobsters the under-side of the rostrum 
is smooth (Fig. 9). In the nomenclature of technical 
zoology, these two kinds or species of Lobster are said 
to constitute (along with a third species found at the 
Cape of Good Hope) the genus Homarus, the 
European species being known as Homarus gam- 



THE LOBSTER AS A TYPE OF CRUSTACEA 33 

marus, and the American as Homarus americanus. 
The so-called " Norway Lobster " or " Dublin 
Prawn," which differs from the Common Lobster in 
having large kidney-shaped eyes and long and 
slender claws, and in many other details of structure, 
is placed in a distinct genus, and is known as Nephrops 
norvegicus. The genera Homarus and Nephrops, 
together with some others, constitute the family 
Homaridae, which again is grouped with other 
families in a tribe, Nephropsidea, forming a part 
of the order Decapoda. These groups are intended 
to express the varying degrees of resemblance and 
difference in structure between the species of animals 
which make up the class Crustacea. Since we have 
good grounds for believing that all these species have 
arisen by some mode of evolution, this classification 
also represents the varying degrees of actual rela- 
tionship between the different forms, so far as this 
relationship can be discovered. In the next chapter 
a brief sketch of the chief subdivisions of the 
Crustacea is given, with such details as to the 
characteristics of each as are necessary to render 
intelligible the succeeding chapters on their habits 
and modes of life. 




CHAPTER III 
THE CLASSIFICATION OF CRUSTACEA 



Table of Classification of Crustacea 
CLASS CRUSTACEA. 



f Order 



Subclass BRANCHIOPODA 

OSTRACODA 
COPEPODA 



Series 



ClRRIPEDIA 

MALACOSTRACA. 
LEPTOSTKACA - 
EUMALACOSTRACA. 
Division Syncarida 



Peracarida 



Eucarida 
Hoplocarida 



I 



Anostraca. 

Notostraca. 

Conchostraca. 

Cladocera. 

Myodocopa. 

Podocopa. 

Eucopepoda. 

Branchiura. 

Thoracica. 

Rhizocephala. 

Nebaliacea. 

Anaspidacea. 

Mysidacea. 

Cumacea. 

Tanaidacea. 

Isopoda. 

Amphipoda. 

Euphausiacea. 

Decapoda. 

Stomatopoda. 



/'OCCASIONALLY there may be found in rain- 
^ ' water puddles and the like, in the South of 
England, a beautiful, transparent, shrimp-like animal, 
an inch or more in length, to which the name of 

34 



THE CLASSIFICATION OF CRUSTACEA 35 

"Fairy Shrimp" has been given (Fig. 10). It is 
known in technical zoology as Chirocephalus di- 
aphanus, and is ' a representative of the subclass 
BRANCHIOPODA. The members of this group are 
distinguished from other Crustacea by their flattened, 
leaf-like feet, each of which is divided into a number 
of lobes, and has a gill plate on the outer side. In 
Chirocephalus there is no carapace, and the head is 
followed by eleven distinct body segments, each 
bearing a pair of leaf-like, or rather fin-like, feet. 




FIG. 10 THE "FAIRY SHRIMP" (Chirocephalus diaphanus), 
MALE, x 2. (After Baird.) 

The hinder part of the body has no appendages, 
and ends in a forked tail. In the female a large 
pouch hangs from the under-side of the body, just 
behind the limb-bearing part, and is often found 
filled with eggs. In the male, a pair of remarkable- 
looking appendages, each shaped somewhat like a 
hand with webbed fingers, hang in front of the head. 
These are connected with the antennae, and are 
known as the " claspers," from their function in 
seizing and holding the female. The eyes are set on 
movable stalks. Those Branchiopoda which, like 



3 6 



THE LIFE OF CRUSTACEA 






Chirocephalus, have no carapace, form the order 
ANOSTRACA. 

A second order, the NOTOSTRACA, is represented 

by Apus cancriformis (Plate II.), which occurs in 

A. 



ad. 




FIG. nEstheria obliqua, ONE OF THE CONCHOSTRACA. 
(After Sars, from Lankester's " Treatise on Zoology.") 

A, Shell of female, from the side ; B, male, from the side, after 
removal of one valve of the shell. (Enlarged.) a', Antennule ; 
a", antenna ; ad, muscle which draws together the valves of the 
shell ; /, tail fork ; ntd, mandible 

many places in Europe in ponds and puddles, and 
very rarely indeed in Britain. In Apus there is a large 



PLATE If 




Apus cancri/bniiis, FROM KIRKCUDBRIGHTSHIRE. (SLIGHTLY ENLARGED) 



THE CLASSIFICATION OF CRUSTACEA 37 






dorsal shield, or carapace, covering the greater part of 
the body, which consists of a large number of seg- 
ments (about twenty- 
eight), and ends be- 
hind in a pair of 
long antenna-like fila- 
ments. The fin-like 
feet are also very nu- 
merous (about sixty- 
three pairs). The eyes 
are not stalked, but 
are set close together 
on the upper surface 
of the carapace. 

The third order of 
the Branchiopoda, 

the CONCHOSTRACA 

(Fig. n), are not re- 
presented in Britain, 
though several 
species occur on the 
Continent of Europe. 

T , , FIG. 12 Daphnia pulex, A COMMON 

In these the cara- SPECIES OF "WATER-FLEA." MUCH 




pace forms a bivalved gSde^ 15 

shell, completely en- Female carrying eggs in the brood- 

closing the body and chamber 

limbs, and closely resembling that of a small mollusc. 
The fourth order, the CLADOCERA, comprises the 
so-called " Water-fleas," which are abundant every- 



38 THE LIFE OF CRUSTACEA 

where in ponds and lakes (Fig. 12). They are all 
of small size, almost or quite microscopic. The 
carapace, as in the Conchostraca, forms a bivalved 
shell, but does not enclose the head. There is a 
single large eye, which really corresponds to two 
eyes fused together. A pair of large antennae, each 
with two branches, carrying long feathered hairs, 
project at the sides of the head, and are used in 

e. 

B. 




FIG. 13 SHELLS OF OSTRACODA. MDCH ENLARGED. (From Lan- 
kester's "Treatise on Zoology," after Brady and Norman, and 
Miiller.) 

A, Philomedes brenda (Myodocopa) ; B, Cypris fuscata (Podocopa) ; 
C, Cytherris ornata (Podocopa). n, Notch characteristic of the 
Myodocopa ; e, the median eye ; a, mark of attachment of the 
muscle connecting the two valves of the shell. A and C are 
marine species ; B is from fresh water 

swimming with a peculiar jumping motion, from 
which the popular name of the animals is derived. 
There are not more than six pairs of feet. The 
" Water-fleas," of which Daphnia pulex is one of the 
commonest species, are very beautiful and interesting- 
objects for microscopic examination, on account of 
their transparency, which allows many details of their 
internal structure to be studied in the living animal. 
The OSTRACODA (Fig. 13), which form the second 



THE CLASSIFICATION OF CRUSTACEA 39 

subclass in the system of classification here adopted, 
are nearly all microscopic animals, and are found 
abundantly in fresh water as well as in the sea. The 
carapace forms a bivalved shell, which completely 
encloses the body and limbs, and is often sculptured 
in an elegant fashion. The Ostracoda are remark- 




FIG. 14 Cyclops albidus, A SPECIES OF COPEPOD FOUND IN 
FRESH WATER. (After Schmeil.) 

Female specimen carrying a pair of egg-packets. The actual 
length is about one tenth of an inch 

able for the very small number of their appendages. 
There are not more than two pairs of limbs behind 
the maxilla. Most of the species are included in two 
orders, the Myodocopa and the Podocopa, of which 
the former may generally be distinguished by a 
notch in the anterior part of the margin of the shell 
(Fig. 13, A, ). In the Podocopa the margin is entire. 






40 THE LIFE OF CRUSTACEA 

The subclass COPEPODA comprises animals, for 
the most part of microscopic size, which are abundant 
in fresh water and in the sea. The common fresh- 
water genus Cyclops (Fig. 14) furnishes a good 
example of the type of structure characteristic of 
the class. The body is somewhat pear-shaped, with 
a narrow abdomen ending in a " caudal fork." The 
body is divided into somites, and there is no over- 
lapping carapace, although the head and the first 
two thoracic somites are coalesced. There are four 
pairs of two-branched, oar-like, swimming feet, and a 
fifth pair, found in some other Copepoda, is repre- 
sented in Cyclops by minute vestiges on the first 
segment of the narrow posterior part of the body. 
The antennules are very large, unbranched and com- 
posed of numerous segments ; the antennae are 
much smaller. In addition to the usual mandibles, 
maxillulae, and maxillae, there is a pair of maxillipeds 
which really represent the first pair of trunk limbs. 
There is a single red eye in the middle of the front 
of the head. This eye is not formed, like the single 
eye of the Cladocera, by fusion of a pair of eyes, but 
it corresponds to a median eye of simple structure 
which is found in the Branchiopoda, Ostracoda, and 
many other Crustacea, in addition to the paired 
compound eyes. From the fact that this median 
eye is the only one present in the earliest larval 
stage of Crustacea, the Nauplius (see Chapter IV.), 
it is sometimes known as the " nauplius eye." The 



THE CLASSIFICATION OF CRUSTACEA 41 

female Cyclops carries her eggs until they hatch, in 
two oval packets attached to the sides of the 
body. 

Forming a separate order (BRANCHIURA) apart from 
the more normal Copepoda (order EUCOPEPODA) is 
the little group of the Carp-lice, one of which, 
A rgulus foliaceus, is common in England, living as a 
parasite on different species of fresh-water fish, and 
often found swimming free in ponds and rivers It 
has a broad, flat, and very transparent body, about 
three-sixteenths of an inch in length. It differs 
from Cyclops in a great many points, of which, 
perhaps, the most conspicuous is the possession of a 
pair of true compound eyes in addition to the 
median eye. On the under-side of the head are a 
pair of large round suckers, by means of which the 
animal fixes itself on to its prey. A study of their 
development shows that these suckers are really the 
maxillae, which in the young animal are jointed 
limbs ending in a strong claw, but later become 
changed into the suckers of the adult. A sharp 
spine, which can be protruded in front of the mouth, 
is connected with what is believed to be a poison- 
gland. The eggs are not carried in packets by the 
female as in Cyclops, but are deposited on stones or 
water-weeds. 

The fourth subclass, CIRRIPEDIA, comprises the 
Barnacles and Acorn-shells. These are very unlike 
any of the other Crustacea, and, in fact, they were 






42 THE LIFE OF CRUSTACEA 

long classed by naturalists with the Mollusca. It 
was not until their larval development was made 
known that they were recognized as Crustacea. 
The common Goose Barnacle (Lepas anatifera 
Plate III.) is found adhering to the bottoms of ships 
and to floating timber. It has a fleshy stalk or 
peduncle which is fixed at one end to the supporting 
object, and bears at the other end a shell, made up 
of five separate plates, enclosing the body of the 
animal. The stalk corresponds to the front part of 
the head, and careful examination may discover at 
its end, among the hardened cement which fixes it 
to the support, the remains of the antennules by 
which the attachment of the young animal was first 
effected. The body of the animal within the cara- 
pace or shell bears the usual mandibles, maxillulae, 
and maxillae, close to the mouth, and six pairs of 
long, tendril-like feet. These feet have each two 
branches, composed of numerous short segments 
and fringed with long hairs. They can be protruded 
from the slit-like opening of the shell, forming a sort 
of " casting-net " for the capture of minute floating 
prey. 

The Acorn-shells, of which one species (Balanus 
balanoides Plate III.) is abundant everywhere on 
our coasts, covering rocks and stones just below 
high-water mark, differ from Lepas and its allies in 
having no peduncle. The shell is cemented directly 
to the rock, and is conical in shape, like a small 



PLATE HI 




x M 

R-S 



5 

m 




THE CLASSIFICATION OF CRUSTACEA 43 

limpet, with a hole at the top which is closed by 
four movable valves. 

The Stalked Barnacles, like Lepas (suborder 
Pedunculata), and the Sessile Barnacles, or Acorn- 
shells, like Balanus (suborder Operculata), together 
form the order THORACICA. Of the other orders 
which compose the subclass Cirripedia, the only one 
that need be mentioned here is the RHIZOCEPHALA, 
which comprises strangely degenerate parasites living 
on other Crustacea. 

The Cirripedia are unlike nearly all other Crus- 
tacea in the fact that, with few exceptions, they are 
hermaphrodite, having both sexes united in each 
individual. In certain species of the Stalked Bar- 
nacles, however, there are minute male individuals 
that are attached, like parasites, to the large her- 
maphrodites. In a few species the large individuals 
only possess female organs, so that the separation of 
the sexes is complete. 

The remarkable larval metamorphoses of Cirripedes 
and the modifications of structure presented by some 
parasitic forms will be described in later chapters. 

The fifth and last subclass, that of the MALACOS- 
TRACA, is by far the largest and most important, and 
will require to be considered in more detail than any 
of the others. The animals composing the various 
orders into which the subclass is divided differ very 
greatly in structure, but they all agree in having 
typically the same number of appendages as the 



44 



THE LIFE OF CRUSTACEA 



Lobster namely, nineteen pairs (or twenty, if the eye- 
stalks be included). They also agree in the very 
important character that the trunk limbs are divided 
into two sets, thoracic and abdominal, the former of 
eight, and the latter of six pairs. 

The first order of the Malacostraca, the NEBA- 
LIACEA, comprises a few Crustacea of small size, 
ad. P- 




FIG. 15 Nebalia bipes. ENLARGED. (From Lankester's 
" Treatise on Zoology," after Claus.) 

a', Antennule ; a", antenna ; atf-ab*, the abdominal limbs ; ad, 
muscle joining the two valves of the shell ; /, tail-fork ; p, palp 
of maxillula ; r, rostral plate ; t, telson ; 1-7, the seven somites of 
the abdomen 

which differ in some very important characters from 
all the other orders. Nebalia bipes (Fig. 15), which 
occurs on the southern coasts of the British Isles, has 
a large bivalved carapace enclosing most of the 
limbs. In front, a small " rostral plate " is joined 
to the carapace by a movable hinge, and partly 
covers the stalked eyes. The eight pairs of thoracic 



THE CLASSIFICATION OF CRUSTACEA 45 

feet are all alike, and are flattened and leaf-like in 
form, resembling those of the Branchiopoda. The 
first four pairs of abdominal limbs are large two- 
branched swimming feet, but the last two pairs are 
reduced to small vestiges. Two of the most impor- 
tant points in which the Nebaliacea differ from all 
the other Malacostraca are that there are seven 
instead of six somites in the abdomen (the last 
somite has no appendages), and that the telson has 
connected with it a pair of movable rods forming a 
" caudal fork " like that of the Branchiopoda. On 
account of the leaf-like thoracic feet and the posses- 
sion of a caudal fork and other features, the Nebaliacea 
were formerly classified with the Branchiopoda, 
but a closer examination of their structure has 
shown that they are true Malacostraca. In having 
an additional somite in the abdomen and in other 
points, however, they may be regarded as forming a 
link between the Malacostraca and the lower forms 
of Crustacea, and for this reason they are set apart 
as a series LEPTOSTRACA, while the other orders 
form a series EUMALACOSTRACA. 

The orders of the Eumalacostraca, again, are 
grouped, as shown in the table of classification, into 
four divisions. The first of these, the SYNCARIDA, 
includes only one order, comprising a few small 
Crustacea (see Fig. 84, p. 264) which have recently 
been discovered in fresh water in Tasmania and 
Australia. They have no carapace, and all the 



46 THE LIFE OF CRUSTACEA 

thoracic somites, or all but the first, are distinct. 
The antennules are two-branched, the antennae may 
have a scale-like exopodite, and the last pair of ab- 
dominal appendages form, with the telson, a tail-fan. 
The eyes are sometimes stalked, but in one species 
they are sessile. The thoracic limbs, which are not 
clearly divided into maxillipeds and legs, carry a 
double series of plate-like gills or epipodites. As 
will be shown later, the living Syncarida are espe- 
cially interesting on account of their resemblance to 
certain very ancient fossil Crustacea. 

The second division of the Eumalacostraca, the 
PERACARIDA, includes five orders, the members of 
which differ very greatly in appearance. They all 
agree, however, in certain important points of struc- 
ture, of which the most conspicuous is the posses- 
sion, in the female sex, of a brood-pouch for carrying 
the eggs and young. This brood-pouch is formed 
by a series of overlapping plates attached to the 
bases of the thoracic limbs. 

The first order of the Peracarida, the MYSIDACEA, 
consists of small, free-swimming, shrimp-like animals 
(Fig. 16). Many species are common in the sea 
round the British coasts, and from their possession 
of a brood-pouch, in which the young are carried, 
they are sometimes known as " Opossum Shrimps." 
The eyes are stalked, and the carapace is well 
developed, although it does not unite with all the 
thoracic somites. The antennae have a flattened, 



THE CLASSIFICATION OF CRUSTACEA 47 

scale- like exopodite, probably of use for keeping the 
animal balanced in swimming. Only one pair of the 
thoracic limbs are modified to form maxillipeds, and 
all the legs (as in the larval Lobster) have exopodites 
which form the chief swimming organs. The uro- 
pods and telson form a " tail-fan." One of the most 
curious points in the organization of some Mysidacea 




FIG. 16 Mysis relicta, ONE OF THE MYSIDACEA. ENLARGED. 
(From Lankester's "Treatise on Zoology," after Sars.) 

cs, Cervical groove of the carapace ; m, brood-pouch 

is the possession of a pair of statocysts in the endo- 
podites of the uropods. Each statocyst consists of a 
small cavity containing a cake-shaped concretion 
known as a " statolith," resting on a group of 
sensory hairs. There is reason to believe that these 
organs have the same function as the statocysts of 
the Lobster, although they are placed at the other 
end of the body. The statolith serves the same 
purpose as the sand-grains found in the Lobster's 
statocyst, although, unlike these, it is not introduced 



48 THE LIFE OF CRUSTACEA 

from outside, but is formed in position by secretion 
from the walls of the sac. 

Most of the Mysidacea have no special organs of 
respiration, that function being discharged (as in 
many of the smaller Crustacea) by the general 
surface of the body, and especially by the thin 
carapace ; but certain deep-sea Mysidacea (Fig. 17) 
have tufted gills attached at the base of the thoracic 




FIG. 17 Gnathophausia willemoesii, ONE OF THE DEEP-SEA MYSI- 
DACEA. HALF NATURAL SIZE. (From Lankester's "Treatise on 
Zoology," after Sars.) 

gr, A groove dividing the last abdominal somite 

legs. In all cases the maxilliped has a plate-like 
epipodite, which lies under the side-fold of the cara- 
pace, and no doubt assists respiration, causing by its 
movements a current of water to flow under the 
carapace. 

The members of the second order of the Pera- 
carida, the CUMACEA (Fig. 18), are small marine 
Crustacea in which the anterior part of the body 
is generally stout, while the abdomen is slender and 
very mobile. The short carapace does not cover 



THE CLASSIFICATION OF CRUSTACEA 49 

more than the first three or four of the thoracic 
somites. The eyes are not stalked, and are usually 
fused together to form a single organ on the front 
part of the head. Swimming branches (exopodites) 
are usually present on some of the thoracic legs, at 
least in the males, which are more active swimmers 
than the females. In the males, also, the swimmerets 
of the abdomen are often more or less developed, 



-t. 




t. 



FIG. 18 Diastylis goodsiri, ONE OF THE CUMACEA. ENLARGED. 
(From Lankester's " Treatise on Zoology," after Sars.) 

a', Antennule ; P--P, the five pairs of walking legs ; m, brood-pouch ; 
ps, " pseudo-rostrum " formed by lateral plates of the carapace ; 
t, telson ; ur, uropods 

but they are always absent in the females. The 
uropods do not form a tail-fan, but are slender 
forked rods carrying comb-like rows of spines, said 
to be used in cleaning the anterior appendages from 
the mud among which these animals generally live. 
The telson is often absent, or, rather, it is coalesced 
with the last somite of the abdomen. Under the 
side-fold of the carapace on each side lies, as in the 
4 



50 THE LIFE OF CRUSTACEA 

Mysidacea, the epipodite of the maxilliped ; but in 
this order it forms a gill, and usually carries a row 
of flattened gill lobes. 

The third Order, that of the TANAIDACEA (Fig. 19), 
is of special interest, since in many respects it forms 
a transition to the next. It comprises a number of 
minute Crustacea, generally found burrowing in mud 
in the sea. They have a small carapace, which only 
involves the first two thoracic somites, the rest of 






FIG. 19 Apseudes spinosus, ONE OF THE TANAIDACEA. EN- 
LARGED. (From Lankester's " Treatise on Zoology," after 
Sars.) 

ex, Vestiges of exopodites on second and third thoracic limbs ; oc, 
the small and immovable eye-stalks ; sc, scale or exopodite of 
antenna ; ur, uropod 

the somites being distinct. The side-folds of the 
carapace enclose a pair of small cavities, within 
which lie, as in the case of the last two orders, 
the epipodites of the maxillipeds. The eyes are not 
movable, although they are set on little side-lobes of 
the head, representing the vestiges of eye-stalks. The 
first pair of thoracic limbs are maxillipeds, and the 
second pair are very large, and form pincer-claws 
(chelae). Minute vestiges of exopodites are some- 




THE CLASSIFICATION OF CRUSTACEA 51 

times found on the second and third pairs, but they 
are not used for swimming, and only help to keep a 
current of water flowing through the gill cavities. 
The abdomen is very short, with small swimmerets, 
and the telson is not separated from the last somite. 
The uropods are generally very 
small, and do not form a tail- 
fan. 

Unlike the Tanaidacea, the 
ISOPODA, which form the fourth 
order of the Peracarida, are 
very numerous in species, and 
very varied in structure and 
habits. The most familiar are 
the Woodlice, or Slaters, which 
are commonly found in damp 
places, under stones and the 
like. Besides these, however, 
the order includes a vast 
number of forms living in the 
sea and a few that live in fresh 
water. The examination of a 
common Woodlouse, such as Oniscus or Porcellio 
(Fig. 20), will give a general idea of the form and 
structure of a typical Isopod, although many curious 
modifications are found, some of which will be men- 
tioned in later chapters. 

There is no distinct carapace, but the last vestige 
of one may be indicated by the fact that the first 




FIG. 20 A WOOD- 
LOUSE (Porcellio 
s caber) , ONE OF 
THE ISOPODA. EN- 
LARGED. (From Lan- 
kester's " Treatise on 
Zoology," after Sars.) 



52 THE LIFE OF CRUSTACEA 

thoracic somite is completely fused with the head. 
All the other somites of the body are distinct (in 
some Isopods, however, the abdominal somites are 
coalesced), but the telson is not separate from the 
last somite. The eyes are not stalked, but are sessile 
on the sides of the head. The antennules have only 
a single branch, and in the Woodlice are very small. 
The antennae have no exopodite, although in a few 
other Isopods a minute vestige is present. The 
thoracic limbs never have any trace of exopodites. 
The first pair are maxillipeds, and if they carry an 
epipodite it is never enclosed in a gill cavity, as in 
Tanaidacea. The swimmerets form one of the most 
characteristic features of the Isopoda, for they are 
always flattened into thin plates, which act as gills. 
In the Woodlice, which breathe air, certain curious 
modifications of the swimmerets are found, which 
will be described in a later chapter. In some 
Isopods that live as parasites on fish or on other 
Crustacea, each individual is at first a male, and later 
becomes a female. They are almost the only Crus- 
tacea, except the Cirripedes already mentioned, 
which are normally hermaphrodite. 

The fifth order of the Peracarida, the AMPHIPODA, 
is also a very large one. The " Sand-hoppers," 
which are very common on sandy coasts, belong to 
this order, as do also a very large number of other 
forms found in the sea and in fresh water, which 
have no popular names. A common species is 



THE CLASSIFICATION OF CRUSTACEA 53 

Gammarus pulex, sometimes called the " Fresh-water 
Shrimp," which is found everywhere in streams 
and ditches. Several closely allied species, such as 
G. locusta, (Fig. 21), are found in the sea. The body 
is flattened from side to side, and the abdomen is 
generally bent upon itself. There is no carapace, 



vm. 



n 



6. 




FIG. 21 AN AMPHIPOD (Gammarus locusta). ENLARGED. (From 
Lankester's "Treatise on Zoology," after Sars.) 

a', Antennule ; a", antenna; ace, accessory (inner) flagellum of anten- 
nule ; br, gill plate ; ex, coxal plate (the expanded first segment 
of the leg) ; gn, the two pairs of gnathopods (prehensile legs) ; 
pip'", abdominal appendage of third pair ; prp', prp", first and 
second peraeopods, or walking-legs ; t, telson ; ur, uropod ; II, 
VIII, second and eighth thoracic somites; i, 6, first and sixth 
abdominal somites 

but, as in the Isopods, the first thoracic somite is 
fused with the head. The eyes are sessile on the 
sides of the head. The antennules have a small 
inner branch, and the antennas have no exopodites. 



54 



THE LIFE OF CRUSTACEA 



The thoracic limbs, of which the first pair form 
maxillipeds, have no exopodites, and are partly 
hidden by a row of shield-like plates along the sides 
of the thorax. These plates are formed by the 
IV. v. 




a. 

FIG. 22 Two SPECIES OF CAPRELLIDJE. (From Lankester's 
"Treatise on Zoology," after Sars.) 

A, Phtisica marina, a species which retains the fourth and fifth pairs 
of thoracic limbs (prp' y prp") ; B, Caprella linearis, in which these 
limbs are represented only by the gills (br). (Enlarged.) a', 
Antennule ; a", antenna ; abd, vestigial abdomen ; gn, gnathopods ; 
m, brood-pouch ; IV, V, fourth and fifth thoracic somites 

enlarged and flattened basal segments of the limbs 
themselves, and on the inner side they carry a series 
of oval plates, which are the gills. The abdominal 



THE CLASSIFICATION OF CRUSTACEA 55 



appendages are divided into two sets : the first three 
pairs have each two slender, many-jointed branches, 
and are used in swimming; the last three pairs 
are short, stiff, and 
directed backwards, 
and are used in 
pushing the animal 
through mud or 
among water-weeds. 
In many Amphipods, 
such as the Sand- 
hoppers, the last 
three pairs of abdo- 
minal limbs are used 
in jumping by sudden 
backward strokes of 
the abdomen. 

Two families of the 
Amphipoda differ so 
much in general ap- 
pearance from the 
others that they de- 
serve mention. The 
Caprellidae (Fig. 22) 
have the body drawn 
out to a thread-like 

slenderness, and the abdomen reduced to a mere 
vestige. The fourth and fifth pairs of thoracic limbs 
are generally absent, though the corresponding gills 




FIG. 23 Paracyamus boopis, THE 
WHALE-LOUSE OF THE H0MP- 
BACK WHALE. (From Lankester's 
"Treatise on Zoology," after 
Sars.) 

A, Male, dorsal view, enlarged ; B, 
the maxillipeds detached and fur- 
ther enlarged, a', Antennule ; a", 
antenna; abd, vestigial abdomen; 
br, gills ; gn, gnathopods ; IV, V, 
fourth and fifth thoracic somites 












56 THE LIFE OF CRUSTACEA 

remain. The animals live in the sea, clambering 
among sea-weeds or zoophytes in a fashion which 
recalls the movements of " looper" caterpillars. The 
Cyamidce, or "Whale-lice " (Fig. 23), are, as the name 
implies, parasites on the skin of whales, and are 
closely related to the Caprellidae. They have, how- 
ever, a broad, flattened body, more like that of an 




FIG. 24 Meganyctiphanes norvegica t ONE OF THE EUPHAUSIACEA. 
TWICE NATURAL SIZE. (From Lankester's "Treatise on 
Zoology.") 

Isopod than an ordinary Amphipod, and their legs 
have strong curved claws with which they cling to 
the skin of their host. 

The third division of the Malacostraca, the 
EUCARIDA, consists of two orders of very unequal 
interest and importance. The first of these, the 
order EUPHAUSIACEA (Fig. 24), comprises only a 
single family of small, shrimp-like Crustacea found 
swimming freely at the surface or in the depths of 



PLATE II' 




THE CLASSIFICATION OF CRUSTACEA 57 

the sea. In these the carapace fuses with all the 
thoracic somites, the eyes are stalked, the antennules 
have two flagella, and the antennae have a broad 
scale. None of the thoracic limbs are modified into 
maxillipeds, and all carry swimming exopodites. 
The uropods and telson form a tail-fan. A single 
series of feathery gills are attached to the bases of 
the thoracic limbs. Nearly all the Euphausiacea 
possess the power of emitting light, and are furnished 
for the purpose with a number of organs which were 
formerly supposed to be " accessory eyes." 

The second order of the Eucarida, the DECAPODA, 
is by far the largest of the orders of Crustacea, and 
it includes all the larger and more familiar members 
of the class. It is necessary, therefore, to give a 
considerably fuller account of its subdivisions than 
has been given in the case of the other orders. 
The typical characters of the Decapoda are well 
illustrated by the Lobster, which has been already 
described. As in the Euphausiacea, the eyes are 
stalked, and the carapace fuses with all the thoracic 
somites. From the Euphausiacea the Decapoda 
differ in the fact that three pairs of the thoracic 
limbs are modified as maxillipeds, the remaining five 
pairs forming the " ten legs " to which the name of 
the order alludes. Further, the gills are arranged 
in more than one series, not all attached to the 
bases of the legs, as in the Euphausiacea, and 
covered over by the side -flaps of the carapace 






THE LIFE OF CRUSTACEA 



instead of being freely exposed. While agreeing in 
these essential characters, however, the members of 
the order Decapoda differ very widely among them- 
selves in structure and in general form, and they are 
classified (in the arrangement adopted here) in two 
suborders, which are again subdivided into sections 
and tribes. 



ORDER DECAPODA. 
Suborder NATANTIA 

,, REPTANTIA. 
Section Palinura 
,, Astacura 

,, Anomura 
Brachyura 



/"Tribe Penaeidea. 

,, Stenopidea. 
( Caridea. 



Scyllaridea. 
Eryonidea. 
Nephropsidea. 
Galatheidea. 
Thalassinidea. 
Paguridea. 
Hippidea. 
Dromiacea. 
Oxystomata. 
Brachygnatha. 
Subtribe Brachyrhyncha. 
,, Oxyrhyncha. 

The suborder NATANTIA includes the numerous 
species of what are commonly known as Prawns 
and Shrimps. These are characteristically powerful 
swimmers, with lightly armoured bodies, more or 
less flattened from side to side, with a thin, saw- 
edged rostrum, and with large swimmerets which are 
the chief organs of swimming ; in addition, some of 
the more primitive Natantia have swimming branches, 
or exopodites, like those of the Euphausiacea, on the 
thoracic legs. This suborder is divided into three 



PLATE V 




THE COMMON SPINY LOBSTER (Palinurus vulgaris), (MUCH REDUCED) 
(From Brit. Mas. Guide) 



THE CLASSIFICATION OF CRUSTACEA 59 

tribes. The Penceidea include the large Prawns of 
tropical seas (Penaus Plate IV.), which have the 
first three pairs of legs provided with chelae, and 
not differing greatly in size. The Stenopidea are a 
small group of forms resembling the Penceidea in 
having chelae on the first three pairs of legs, but the 
third pair are much larger than the others. The 
Caridea comprise our common Prawns (Leander, 
Pandalus) and Shrimps (Crangori), besides a host of 
less generally known forms ; in these the third legs 
are never chelate, although the first and second 
often are. 

The second suborder, that of the REPTANTIA, 
is much more diversified, but the animals composing 
it are united by certain characteristics, of which the 
most obvious are their creeping habits (although 
some species can swim well), their heavily armoured 
bodies, often more or less flattened from above 
downwards, with the rostrum never thin and saw- 
edged, and the swimmerets not used to any great 
extent for swimming. 

The first section of the Reptantia, the Palinura, 
includes the Spiny Lobsters, Rock Lobsters, or Sea- 
Crawfish, and their allies, forming the tribe Scylla- 
ridea. They are distinguished by having no large 
pincer-claws, though the last pair of legs may have 
small pincers in the female sex. One species, the 
Common Spiny Lobster (Plate V.), is found ion the 
southern and western coasts of the British Islands. 









60 THE LIFE OF CRUSTACEA 

The other tribe belonging to this section is the 
Eryonidea, comprising a number of small lobster-like 
forms living in the deep sea. They have pincer- 
claws on the first four, or on all five, pairs of legs, 
and they are of special interest on account of their 
geological antiquity. 

The section Astacura contains only a single tribe, 
Nephropsidea, formed by the true Lobsters and the 
fresh-water Crayfishes. They have pincer-claws on 
the first three pairs of legs, and the first pair are 
much larger than the others. 

The third section of the Reptantia, the Anomura, 
comprises forms in which the abdomen is variously 
modified, being either bent upon itself or, if extended, 
more or less soft and feebly armoured. The last pair 
of legs are commonly reduced in size, and not used 
in walking. The members of the four tribes com- 
posing the section differ widely in their general 
appearance. 

The Galatheidea (Plate VI.) are small, flattened, 
lobster-like animals which have the abdomen bent 
under the body. In one family (Porcdlanidce) the 
animals have quite the appearance of little Crabs 
(see Fig. 41, p. 113), but they may be distinguished 
from the true Crabs (Brachyura) by the fact that 
there are only three pairs of walking legs behind the 
great chelae, the last pair of legs being very small 
and carried folded up at the sides of the body, or 
even within the gill chambers. 



PL ATE VI 




Munida rugosa. BRITISH. (REDUCED) 



THE CLASSIFICATION OF CRUSTACEA 61 

The Thalassinidea are small lobster - like animals 
which burrow in sand and mud, and have generally 
a more or less soft abdomen (see Fig. 38, p. 103). 

The tribe Paguridea includes the Hermit Crabs 
(Pagurid<z) and their allies. The typical Hermit 
Crabs (Plate VII.), which are familiar objects in 
seaside rock-pools, live in the empty shells of Whelks 
and other Gasteropod Molluscs, which they carry 
about with them as portable shelters. The structure 
of the animals is modified in adaptation to this 
curious habit. The abdomen, which is protected 
during life by the borrowed shell, is soft and 
unarmoured, and is spirally twisted. The swim- 
merets, which have only the function of carrying 
the eggs in the female, are much reduced, and are 
usually present only on one side of the body. The 
uropods no longer form a tail-fan, but are adapted 
for firmly wedging the hind part of the body into 
the coils of the shell. One of the chelipeds is much 
larger than the other, and serves to block up the 
opening when the animal withdraws into its shelter. 
In tropical countries certain Hermit Crabs (Cot.no- 
bitidcE) have become adapted to a life on land, and 
one of these, the well-known Coconut Crab, or 
Robber Crab (Birgus latro), which is the largest 
species of the tribe, has given up the habit of 
protecting itself with a shell, and its abdomen has 
again acquired a strong armour on the upper side. 
The marine Lithodida to which the British Stone 



62 THE LIFE OF CRUSTACEA 

f* 

Crab, Lithodes maia (Plate VIII.) belongs seem at 
first sight to have little resemblance to the Hermit 
Crabs, for they have the abdomen very small, and 
tucked up under the body as in the true Crabs. 
Like the Porcellanidae, mentioned above, however, 
the Lithodidae have only three pairs of walking legs 
behind the chelipeds, the last pair being feeble and 
usually folded out of sight within the gill chambers. 
The relationship of the Lithodidse to the Hermit 
Crabs is shown by the abdomen, which is more or 
less twisted to one side, and has swimmerets only on 
one side in the female, and quite wanting in the male. 

The Hippidea are curious little Crabs found burrow- 
ing in sandy beaches in the warmer seas. They 
have the abdomen tucked under the body, and the 
legs flattened for shovelling the sand. 

The BRACHYURA, or true Crabs, form the fourth 
section of the Reptantia, and are distinguished by 
having the abdomen reduced to a tail-flap, which is 
doubled up under the cephalothorax, and is usually 
without any trace of the uropods which are present 
in all the groups already mentioned, with the single 
exception of the Lithodidae. At the sides of the 
head the side-plates of the carapace become firmly 
soldered to the " epistome," a plate which lies in 
front of the mouth, and in this way there is formed 
the " mouth-frame," within which lie the jaws, 
covered in by a pair of " folding-doors " formed by 
the flattened third maxillipeds. 






PLATE VII 




PLATE VI II 




THE CLASSIFICATION OF CRUSTACEA 63 

The first tribe of the Brachyura, the Dromiacea, 
comprises a number of Crabs that in many points of 
structure resemble the Lobsters, and are regarded as 
the most primitive members of the section. Dromia 
vulgaris (Plate IX.), a furry, clumsy-looking Crab, 
occasionally found on our southern coasts, has the 
last two pairs of legs short and carried up over the 
back, where they are used for holding a mass of 
living sponge which the Crab uses as a cloak to pro- 
tect and conceal itself. At the sides of the abdomen, 
wedged in between the telson and the last somite, 
a pair of small plates may be seen, which are the 
last vestiges of the uropods. These are wanting in 
the other tribes of the Brachyura. 

The Oxystomata (Plate X.), which form the second 
tribe of the Brachyura, are distinguished by the 
form of the mouth-frame, which is narrowed in front 
so as to be triangular instead of square in outline. 
The passages through which the water passes out 
from the gills, which in other Crabs open at the 
front corners of the mouth-frame, are carried for- 
wards to the front of the head. The Oxystomata 
are most abundant in tropical seas, but are repre- 
sented on the British coasts by species of Ebalia, 
small and compact Crabs which are not unlike 
pebbles of the gravel among which they live. 

The remaining Crabs form the tribe Brachygnatha, 
in which the mouth-frame and the maxillipeds that 
close it are more or less quadrilateral in shape. 



64 THE LIFE OF CRUSTACEA 

The tribe is divided into two subtribes, which may 
be recognized by the general shape of the carapace. 
In the Brachyrhyncha this is generally rounded or 
square-cut in front, without a projecting rostrum. 
In this subtribe are included the great majority 
of Crabs. The Edible Crab and the Shore Crab 
(Plate IX.) are familiar examples. In the Oxy- 
rhyncha, on the other hand, the carapace is generally 
narrowed in front, with a projecting rostrum, either 
simple or forked, and is often armed with spines. 
In this subtribe are included the long-legged Spider 
Crabs, several species of which are common on our 
coasts. The Giant Spider Crab of Japan (Plate XI.) 
is the largest of living Crustacea. 

The last division of the Eumalacostraca, the 
HOPLOCARIDA (Plate XII.), is one of very small 
extent, comprising only a single order (Stomatopoda) 
of very remarkable Crustacea which are common 
in tropical seas, and of which at least one species, 
Squilla desmarestii, is occasionally captured on the 
south coast of England. The Stomatopoda are 
prawn-like Crustaceans, usually with a flattened 
body, and are easily recognized by the form of the 
large claws (the second pair of thoracic limbs), in 
which the last segment shuts down, like the blade 
of a pocket-knife, on the preceding segment, and 
forms a very efficient weapon, so that the larger 
species are not to be handled without caution. The 
resemblance of these claws to those of the mantis- 



THE CLASSIFICATION OF CRUSTACEA 65 

insect of Southern Europe led to a common 
Mediterranean species receiving long ago the name 
Squilla mantis (Plate XII.). 

The Stomatopoda have a small carapace, which 
does not cover the last four thoracic somites, and 
has in front a small flattened rostrum, attached 
by a movable hinge, like that of the Leptostraca. 
The eyes are stalked, and, like the antennules, are 
attached to a separate movable segment of the front 
part of the head a peculiarity not found in any 
other Crustacea. There are small plate-like gills 
attached to the bases of some of the thoracic limbs, 
but the chief organs of respiration are large feathery 
gills attached to the pleopods or swimmerets. 

The Stomatopoda are all found in the sea, gener- 
ally in shallow water, burrowing in sand or hiding in 
crevices of rocks or corals. Some species are more 
than a foot in length. 










CHAPTER IV 
THE METAMORPHOSES OF CRUSTACEA 

THE great majority of Crustacea are hatched 
from the egg in a form very different from that 
which they finally assume, and reach the adult state 
only after passing through a series of transformations 
quite as remarkable as those which a caterpillar 
undergoes in becoming a butterfly, or a tadpole in 
becoming a frog. Many of these young stages were 
known for a long time before their larval nature 
was suspected, and it is one of the curiosities of the 
history of zoology that, even after the actual changes 
from one form to another had been observed and 
described in several Crustacea, many eminent 
naturalists refused to believe in the possibility of 
their occurrence. This scepticism was largety due 
to the fact that the common fresh-water Crayfish, 
when hatched from the egg, has practically the same 
structure as the adult, and it was assumed that other 
Crustacea were developed in a similar fashion. 
Although certain cases of metamorphosis had been 
actually seen and described by naturalists in the 
eighteenth century, these observations were for- 

66 



THE METAMORPHOSES OF CRUSTACEA 67 

gotten or misunderstood till they were confirmed 
by Mr. J. Vaughan Thompson, a naval surgeon 
stationed at Cork, the first part of whose " Zoological 
Researches " was published in 1828. Thompson's 
statements were much disputed at the time, but they 
have been confirmed by subsequent research, and it 
is now known that the majority of Crustacea undergo 
a more or less extensive metamorphosis after leaving 
the egg, although, as will be seen later, there are 
many important exceptions to this rule, 

If a fine muslin net be towed at the surface of the 
sea on a calm day, and the contents turned out into 
a jar of sea- water, it will usually be found to have 
captured, among other things, clouds of animated 
specks, which dance in the water or dart hither and 
thither with great rapidity. Many of these specks, 
when examined with the microscope, will be found 
to be Crustacea. Besides adult animals belonging 
to various groups, such as the Copepoda, which pass 
the whole of their life swimming near the surface of 
the sea, there will be numerous larval stages of species 
which in their adult form live on the sea-bottom. 
The identification of the species to which the various 
larvae belong is a matter of considerable difficulty, 
and, although the general course of development is 
now well known for all the chief groups of Crustacea, 
there are very many even of the common British 
species in which the larval transformations have not 
yet been worked out in detail. 



68 



THE LIFE OF CRUSTACEA 






As an example of the larval history of the higher 
Crustacea, we may take the case of the Common 
Shore Crab, Carcinus mcznas (Fig. 25). The young 
stages are common in tow-net gatherings round the 








FIG. 25 LARVAL STAGES OF THE COMMON SHORE CRAB (Carcinus 
mfcnas SEE PLATE IX.). (Partly after Williamson.)' 

A, Young zoea, shortly after hatching; B, megalopa stage; 
C, young Crab. A x 20, B and C x 10 

British coasts in the summer-time. The youngest 
larvae (Fig. 25, A) are translucent little creatures 
about one-twentieth of an inch long. They have 
the head and front part of the body covered by a 
helmet-shaped carapace, with a long spine standing 



PL A TE IX 




THE COMMON SHORE-CRAB (Carciniis iiKenas). (REDUCED) 




Dromia vulgatis, CARRYING ON ITS BACK A MASS OF THE SPONGE Clione celata. 
BRITISH. (REDUCED) 



THE METAMORPHOSES OF CRUSTACEA 69 

out from the middle of the back, and another pro- 
jecting, like a beak, in front. 

The narrow abdomen or tail is very flexible, and 
can be doubled up under the body or stretched out 
behind; it ends in a forked telson. There are two 
pairs of swimming limbs, each with endopodite and 
exopodite, and the short antennules and antennae 
are seen on either side of the rostrum. There are a 
pair of very large compound eyes, which are not set 
on movable stalks, but are under the front part of 
the carapace. The two-branched swimming feet are 
really the first and second maxillipeds (the mandibles, 
maxillulae, and maxillae, can be found in front of 
them), but none of the other thoracic limbs are yet 
developed, and, although the somites of the abdomen 
are distinct, there are no swimmerets. This type of 
larva is known as a zoea, a name which was given 
to it when it was supposed to be an independent 
species of Crustacean. As a matter of fact, the zoea 
just described is not quite the earliest stage of the 
Shore Crab, for when hatched from the egg it is 
without the spines on the carapace, and is slightly 
different in other respects. A few hours after hatch- 
ing, however, it casts its skin for the first time, and 
becomes a fully-formed zoea. It swims rapidly about 
at the surface of the sea, feeding on the minute 
floating animals and plants which are found there,' 
and growing in size with repeated castings of its 
skin. In the later stages of the zoea the rudiments 



70 THE LIFE OF CRUSTACEA 

of the hinder thoracic limbs and of the swimmerets 
appear as little buds. In the next stage (Fig. 25, B) 
all the appendages are present, the dorsal spine of 
the carapace has disappeared, the eyes are stalked 
and movable, and the animal has all the appearance 
of a little Crab, except that the abdomen is stretched 
out instead of being tucked up under the body, and 
the swimmerets are used as paddles in swimming. 
In this stage the larva, which is known as a m'egalopa, 




FIG. 26 LAST LARVAL STAGE OF THE COMMON PORCELAIN- 
CRAB (Porcellana longicornis SEE FIG. 41, p. 113). x 9. (After 
Sars.) 

swims at the surface of the sea, but later it sinks to 
the bottom, and, moulting again, appears as a little 
Crab (Fig. 25, C), with tucked-up abdomen and 
swimmerets no longer adapted for locomotion. 

Most of the true Crabs (Brachyura) have a larval 
history similar to that just described, and pass 
through zoe'a and megalopa stages which differ only 
in details from those of Carcinus. The Anomura are 
also hatched as zoeae, and one of the most remark- 
able forms common in tow-nettings in British waters 
is the zoea of the little Porcelain Crabs (Porcellana 
Fig. 26). In this larva the carapace has two long spines 



THE METAMORPHOSES OF CRUSTACEA 71 

behind, and a rostral spine which is several times 
as long as the body of the animal. A great develop- 
ment of spines also 
characterizes the larva 
of Munida (Fig. 27). 

The larval form of 
the Common Lobster 
has already been, de- 
scribed, and it will be 
noticed that the dif- 
ferences from the 
adult are much less 
than in the case of 
the Crab. From the 
fact that this larva 
has swimming exopo- 
dites on its legs, like 
the adult Mysidacea 
and Euphausiacea 

(formerly grouped to- FIG. 27 FIRST LARVAL STAGE OF 
t . -> i Munida rugosa (SEE PLATE VI.). 

gether as Schizo- x I0 . (After Sars.) 

poda "), it is said to 

be in the " schizopod stage." The larva of the 
Norway Lobster (Nephrops norvegicus) is essentially 
of the same type, but the great development of the 
spines on the abdomen and of the forked telson 
gives it a -striking appearance. 

A very remarkable type of larva is found among 
the Spiny Lobsters and their allies (Scyllaridea). 




72 THE LIFE OF CRUSTACEA 

This larva, known by the name of phyllosoma 
(Fig. 28), is very broad, thin, and leaf-like, and 
quite transparent, so that some of the larger kinds 
were formerly known as " Glass Crabs." The thin 
oval carapace does not cover the whole of the 
thoracic region, which is disc-shaped, with four pairs 




FIG. 28 THE PHYLLOSOMA LARVA OF THE COMMON SPINY 
LOBSTER (Palinurus vulgaris SEE PLATE V.). MUCH ENLARGED. 
(After J. T. Cunningham.) 

of long slender legs, each with an exopodite. The 
abdomen is relatively small. The intermediate 
stages between the phyllosoma and the adult are 
still very imperfectly known. In tropical seas 
phyllosoma larvae of large size are found, sometimes 
reaching two or three inches in length. The larva 
of the Common Spiny Lobster (Palinurus vulgaris}, 
however, does not exceed half an inch in length. 



PLA TE 




THE METAMORPHOSES OF CRUSTACEA 73 

The Shrimps and Prawns of the tribe Caridea are 
mostly hatched as zoeae, and pass through a " schizo- 
pod" stage comparable to that of the Lobster, in 
which they swim by means of exopodites on the legs. 
Some of the Prawns belonging to the tribe Penaeidea, 
however, have a still more remarkable metamorphosis, 
which is very important on account of the resem- 
blance of the earlier stages to those of the lower 
Crustacea. Fritz M tiller discovered in 1863 that 
Penceus is hatched from the egg as a Nauplius 
(Fig. 29, A), a form of larva which was previously 
known among the Copepoda, Branchiopoda, and 
Cirripedes. The nauplius, unlike the larvae which 
we have been considering, has an unsegmented body t 
and has only three pairs of limbs. The body is 
pear-shaped in outline, and near the front end is 
seen the median eye, sometimes called, from its 
presence in this type of larva, the " nauplius-eye "; 
the paired eyes are not yet developed. The three 
pairs of limbs are shown by their later development 
to be the antennules, antennae, and mandibles ; the 
first pair are unbranched, the second and third 
divided into exopodite and endopodite. It is in- 
teresting to notice that the antennas and mandibles, 
which in the adult animal are so widely different 
that it is difficult to trace any resemblance between 
them, are in the nauplius almost identical in form. 
Further, the antennae, instead of being placed in 
front of the mouth as in the adult, lie on either side 



74 



THE LIFE OF CRUSTACEA 



of it, and each has at its base a hooked spine which 
projects inwards and serves for seizing particles of 
food and passing them into the mouth ; the antennae 
of the nauplius, in fact, serve as jaws, while it is 
only later that the mandibles take on this function. 




FIG. 29 LARVAL STAGES OF THE PRAWN Pencils (SEE 

PLATE IV.). x 45. (After F. Miiller.) 

A, Nauplius ; B, young zoea ; C, older zoea ; D, early " schizopod " 
stage 

In the further development of the larva, the body 
increases in length and becomes divided into somites 
which increase in number by new somites appear- 
ing behind those already marked off ; the rudiments 



THE METAMORPHOSES OF CRUSTACEA 75 

of the limbs also appear in regular order from before 
backwards ; the dorsal shield of the nauplius grows 
out into a carapace, beneath which the paired eyes 
begin to develop in front. Thus after passing 
through metanauplius and protozoea stages (Fig. 29, B) 
the larva becomes a zoea (Fig. 29, C), resembling that 
of the Crab already described in that the swimming 
organs are the maxillipeds, but differing in having 
the uropods well developed and forming a tail-fan at 
the end of the abdomen, the hinder thoracic somites 
marked off and their appendages present as rudi- 
ments, and the stalked eyes free from the carapace. 
This is followed by a schizopod stage (Fig. 29, D), in 
which the prawn-like shape is assumed and the 
thoracic legs have large exopodites used for swim- 
ming. Later these exopodites diminish in size, 
though they do not quite disappear in the adult 
Penceus, and the function of swimming organs is 
taken over by the abdominal swimmerets. 

In Penceus the larvae are of comparatively simple 
form, but in the allied genus Sergestes the zoea has 
a very remarkable appearance. The carapace is 
armed with long spines, each bearing two comb-like 
rows of secondary spines. The development of 
spines and other outgrowths of the surface of the 
body is a very common characteristic of organisms 
that, like these larvae, float or swim in the open sea ; 
its probable significance will be discussed in a later 
chapter. 



76 THE LIFE OF CRUSTACEA 

The shrimp-like Euphausiacea have a larval 
development very like that of Penaus. Most, if not 
all, of the species are hatched from the egg in the 
nauplius stage, and pass through stages very similar 
to those described above. The adult animals, how- 
ever, may be said to remain in the " schizopod " 




FIG. 30 NEWLY-HATCHED YOUNG OF A CRAYFISH (Astaciis 
fluviatilis). ENLARGED 

stage, since the exopodites of the thoracic legs remain 
large and are used in swimming. 

Even among the Decapoda, however, there are 
many species that are hatched from the egg in a form 
that does not differ essentially from the adult, and 
are therefore said to have a direct development. 
This is often the case with species which live in 
fresh water or in the depths of the sea. For 
example, the young of the fresh-water Crayfish 



PL A TE XI 



\ 




THE METAMORPHOSES OF CRUSTACEA 77 

(Fig. 30), when hatched, possess all the appendages 
of the adult except the first pair of swimmerets and 
the uropods, or outer plates of the tail-fan. The 
carapace is almost globular, owing to the presence 
inside the body of a large amount of food-yolk, 
which supplies the nourishment necessary for the 
young animal in the early stages of its development. 
The chelae have hooked tips, by means of which the 
young animal clings securely to the swimmerets of 
the mother. After a time it moults, and the uropods 
are set free, the chelae lose their hooked tips, the 
carapace assumes nearly its final shape (the food- 
yolk having been largely absorbed), and the young 
Crayfish leaves the protection of its parent, to shift 
for itself. The essential point of difference between 
the development of the Crayfish and that of the 
closely related Lobster (see Fig. 8, p. 28) is not so 
much that the changes in structure which occur 
after hatching are less profound in the former case, 
but that there is no free larval stage. In the 
Lobster the earlier stages are capable of indepen- 
dent existence, and they differ from the full-grown 
animal not only in structure, but also in habits, 
swimming at the surface instead of creeping at the 
bottom of the sea. 

A similar case to that of the Crayfishes is found in 
the River Crabs of tropical countries, belonging to 
the family Potamonidaa These Crabs Are as closely 
related to some marine Crabs as are the Crayfishes 



78 THE LIFE OF CRUSTACEA 

to the Lobsters, yet the difference in their mode of 
development is even more pronounced. Instead of 
beginning life as minute pelagic zoeae, they leave the 
shelter of the mother's abdomen as perfectly- formed 
little Crabs (Fig. 31). 

Amongst the Decapoda, instances of direct develop- 
ment like those just described are exceptional, but in 
some of the other orders of the Malacostraca direct 
development is the rule. In the great division 
Peracarida, as we have already seen, the females are 




FIG. 31 YOUNG SPECIMEN OF AN AFRICAN RIVER CRAB (Potamon 
johnstoni), TAKEN FROM THE ABDOMEN OF THE MOTHER. 

MUCH ENLARGED 

The adult of an allied species is figured on Plate XXV 

provided with a pouch, or marsupium (from which 
the name of the division is derived), in which the 
eggs are carried. Within this pouch the young 
undergo the whole of their development, and they 
only leave it, as a rule, when they have attained the 
structure of the adults. Among the more familiar 
representatives of this division, the Sand-hoppers 
(Amphipoda), the Woodlice (Isopoda), and the 
Opossum Shrimps (Mysidacea), may be mentioned 



THE METAMORPHOSES OF CRUSTACEA 79 

as examples of this mode of development. The 
Woodlice and their immediate allies differ a little 
from the other members of the division in the fact 
that the young leave the brood-pouch with the last 
pair of legs still undeveloped, though in other 
respects they are like miniature adults. 

In those Crustacea which have a direct develop- 
ment without free-swimming larval stages, it is 
sometimes possible to find traces of such stages in 
the early development of the embryo. This is 
shown most clearly, perhaps, in the Opossum 
Shrimps (Mysidacea). In these the embryo be- 
comes free from the egg-membrane (or may, in a 
sense, be said to " hatch ") at a very early stage, and 
lies free within the brood-pouch as a maggot-shaped 
body, on which three pairs of rudimentary limbs can 
be made out. The later development shows that 
these three rudiments correspond to the antennules, 
antennae, and mandibles, so that the maggot-shaped 
embryo is, in fact, a disguised nauplius without the 
power of swimming or of leading an independent 
existence. In other cases as, for instance, in the 
Crayfish, where the earlier stages are confined 
within the egg-membrane (or " egg-shell ") the 
nauplius stage, although more difficult to examine, 
is quite as well marked. 

Of the other groups of the Malacostraca, the Syn- 
carida and Leptostraca are hatched in nearly the 
adult form, but the Stomatopoda have a long series 



8o 



THE LIFE OF CRUSTACEA 



of larval stages. These larvae (Fig. 32) are all dis- 
tinguished by the large size of the carapace, which 
in some cases envelops the greater part of the body. 
Some stomatopod larvae, in the warmer seas, attain 

to a relatively great 
size, sometimes exceed- 
ing 2 inches in length, 
and their glass-like 
transparency gives them 
a very striking appear- 
ance. 

As we have seen, it 
is exceptional to find a 
free-swimming nauplius 
larva among the Mala- 
costraca, but it is the 
commonest larval stage 
in the other subclasses 
of Crustacea. Most of 
the Branchiopoda are 

hatched in this form 
TIG. 32 EARLY LARVAL STAGE 

OF A SPECIES OF SQUILLA, PROB (Fig. 33), and reach the 

ABLY S. dubia. X 10. (After , , , 

Brooks .) adult state by a very 

gradual series of 

changes in which new somites and appendages are 
added in regular order from before backwards till the 
full number is reached. The Water-fleas (Cladocera), 
however, differ from most of the uther Branchiopoda 
in having a direct development. The eggs are 




THE METAMORPHOSES OF CRUSTACEA 81 

carried in a brood-pouch under the back of the 
carapace, and in this the embryos undergo their 
development. In the common Daphnia, for instance, 
numerous eggs or young can generally be seen 
through the transparent carapace (see Fig. 12, p. 37). 




FIG. 33 LARVAL STAGES OF THE BRINE SHRIMP (Artemia 
salina). (After Sars.) 

A, Nauplius, just hatched ; B E, later stages, showing progressive 
increase in number of somites and appendages. The adult 
form of this species is shown in Fig. 55, p. 164 

Many of the Ostracoda have a direct development, 
but in some cases the young animal, on hatching, 
6 



82 THE LIFE OF CRUSTACEA 

has only the first three pairs of appendages, and is 
therefore regarded as a nauplius, although it possesses 
a bivalved shell like that of the adult, and is very 
unlike the nauplius larvae of other Crustacea. 

Most of the Copepoda also leave the egg in the 
nauplius stage ; and, indeed, it was to the young of 
the common fresh-water Cyclops (Fig. 34) that the 
name of Nauplius was first given by the Danish 




FIG. 34 EARLY NAUPLIUS LARVA OF A COPEPOD (Cyclops). MUCH 
ENLARGED. (From Lankester's " Treatise on Zoology.") 

a', Antennule ; a", antenna ; gn, jaw-spine of antenna ; Ibr, upper 
lip ; md, mandible 

naturalist, O. F. Muller, in the eighteenth century, 
in the belief that it was an adult and independent 
species of Crustacea. In the Copepoda, the changes 
which transform the nauplius into the adult are 
gradual, and consist chiefly in the successive addition 
of new somites and appendages. 

The development of the Cirripedia is of special 



PLATE XII 




Squilla mantis, FROM THE MEDITERRANEAN. 

ABOUT ONE-HALF NATURAL SIZE 
(From Brit. Jlfus. GtiMe) 



THE METAMORPHOSES OF CRUSTACEA 83 

interest, since it was the discovery of the larval 
stages by J. Vaughan Thompson that first demon- 
strated to naturalists that the Barnacles were 
Crustacea and not, as had been supposed, Molluscs. 



B. 




FIG. 35 LARVAL STAGES OF THE COMMON ROCK BARNACLE 
(Balanus balanoides SEE PLATE III.) 

A, Nauplius stage (after Hoek) ; B, cypris stage (after 
Spence Bate) 

The earliest stage is generally a nauplius (Fig. 35, A) 
of very peculiar and characteristic form, with a pair 
of horns projecting sideways from the front corners 
of the dorsal shield, and a forked spine on the under- 



84 THE LIFE OF CRUSTACEA 

side behind. The later development is very unlike 
those which have been described above, for after a 
series of nauplius stages the larva passes suddenly, 
at a single moult, into a stage in which the body 
and limbs are enclosed in a bivalved shell (Fig. 35, B). 
From the superficial resemblance of the shell to that 
of an Ostracod, this is known as the cypris stage. 
Through the valves of the shell a pair of large com- 
pound eyes can be seen, as well as six pairs of 
two-branched swimming feet, while in front a pair 
of antennules project between the valves. On each 
antennule is a sucker-like disc by means of which 
the larva, after swimming freely for some time, 
attaches itself to a stone or some other object, where 
it remains fixed for the rest of its life. A cementing 
substance produced by a gland at the base of the 
antennules attaches the front part of the head firmly 
to the support ; the valves of the shell are cast off, 
and replaced by the rudimentary valves of the adult 
shell ; the six pairs of swimming feet grow out into 
tendril-like cirri ; the compound eyes disappear, and 
the animal assumes the structure of the adult. 

The parasitic Rhizocephala have a very remark- 
able life-history, which will be described in a later 
chapter ; but it may be mentioned here that their 
free-swimming larval stages resemble very closely 
those of the ordinary Barnacles. It was the dis- 
covery of this fact which led to its being recognized 
that the Rhizocephala are highly modified and 



THE METAMORPHOSES OF CRUSTACEA 85 

degenerate Cirripedes, although their structure in 
the adult state gives little evidence of their affinities. 

A number of interesting problems in specula- 
tive biology are suggested by the larval stages of 
Crustacea. A full discussion of these problems 
would involve matters too technical for these pages, 
but some indication of the broader issues may be 
attempted. 

The obvious question, Why do some Crustacea 
pass through a complicated metamorphosis while 
others do not ? is, like many obvious and simple 
questions, one of the most difficult to answer. It 
will be pointed out later, in dealing with the fresh- 
water Crustacea, that one of the most general 
characters of fresh-water animals as compared with 
their marine allies is the absence of free-swimming 
larval stages. This applies, for instance, to the case 
of the Crayfishes and the marine Lobsters, and to 
that of the River Crabs, as compared with those 
which live in the sea. But it does not apply to all 
fresh-water Crustacea, and, on the other hand, there 
are many cases of direct development in marine 
species. 

Some of the advantages gained by the possession 
of free-swimming larval stages are obvious enough. 
Many Crustacea which live on the sea-bottom, and 
are not very powerful swimmers, have their progeny 
scattered far and wide by winds and currents while 
in the surface-living larval stages. In the extreme 



86 THE LIFE OF CRUSTACEA 

case of the Barnacles, which are fixed to one spot 
when adult, a locomotive larval stage is clearly a 
necessity. But, here as elsewhere, to demonstrate 
the usefulness of any character is to go only a very 
little way towards explaining its origin. Moreover, 
the mere necessity for a locomotive larva throws no 
light on the remarkable resemblances between the 
larval stages of widely different species. In the 
adult state, a Branchiopod, a Copepod, an Ostra- 
cod, a Barnacle, and a Penaeid Prawn, are separated 
by enormous differences of form and structure ; yet, 
as we have seen, all these are hatched from the egg 
as six-limbed nauplius larvse differing from each 
other only in trivial details. It seems hardly possible 
to imagine any other interpretation of this very 
striking fact than is afforded by the theory of Evolu- 
tion. We are forced to assume that all these diverse 
forms of Crustacea are descended from very similar 
or identical ancestral types, and that the modifica- 
tions arising in the course of their evolution have 
affected the adult but not the larval stages. Some 
naturalists would go farther than this, and would 
apply the so-called "theory of recapitulation" to 
the larval stages of the Crustacea. According to 
this theory, the stages in the development of any 
animal tend to recapitulate, more or less closely, the 
history of the race. Thus it is assumed, for instance, 
that the nauplius reproduces the structure of a six- 
limbed ancestral form, from which, in the distant 



THE METAMORPHOSES OF CRUSTACEA 87 

past, all the diverse branches of the Crustacean 
class took their origin. There are, however, con- 
siderable difficulties in the way of this view. That 
some such ancestral type did exist may be regarded 
as tolerably certain ; that it resembled in its adult 
state the nauplius larvae of present-day Crustacea 
is, on the whole, unlikely ; but it is not at all 
improbable, whatever its adult structure may have 
been, that it hatched from the egg as a nauplius 
larva. 

With regard to some of the other larval forms, 
it is possible to speak with a little more confidence. 
There are good grounds for believing, apart from the 
evidence of development, that the Lobster and its 
allies have descended from Crustacea which, like the 
existing Euphausiacea, possessed swimming branches 
(exopodites) on the thoracic legs ; and there seems 
no reason to doubt that the " schizopod " larva of 
the Lobster does recapitulate this stage in the evolu- 
tion of the race. On the other hand, it is impossible 
to believe that any of the ancestors of the Shore 
Crab resembled, even remotely, the zoea stage with 
which the life-history of the individual now begins. 



CHAPTER V 

CRUSTACEA OF THE SEASHORE 

tract of seashore which is laid bare by the 
A retreat of the tide offers on most coasts a rich 
collecting-ground to the student of Crustacea. In 
places where shelving, weed-covered rocks run out to 
sea, innumerable Crustacea have their home in the 
rock-pools, or lurk in crannies awaiting the return of 
the tide. On sandy beaches, at first sight apparently 
barren of life, a closer search will reveal a whole 
fauna, amongst which burrowing Crustacea of various 
orders are prominent. Further, the shore collector 
will find from time to time stray specimens of forms 
that have their proper habitat beyond low-tide mark, 
and occasionally their remains are thrown in quan- 
tities on the beach by storms. It is convenient, 
therefore, to treat the Crustacea of the shore as a 
sample of those inhabiting the shallower waters of 
the ocean. In these shallower waters down to the 
limit where light no longer penetrates from above, 
where vegetable life ceases, and where the strangely 
modified inhabitants of the deep sea begin to appear 

88 



CRUSTACEA OF THE SEASHORE 89 

the sea-bottom is perhaps the most densely popu- 
lated of all parts of the earth's surface. Nowhere, 
at all events, do we find so wide a range of animal 
forms, from the simplest organisms (Protozoa) up to 
highly-organized Vertebrates. Nowhere, perhaps, is 
the struggle for existence more keen, and it is not 
without justice that some naturalists have regarded 
the shallow waters of the sea as " one of the great 
battle-fields of life," where, in the long course of 
evolution, the main branches of the animal kingdom 
have had their origin. 

Conspicuous among the animals of this region are 
Crustacea of all sorts and sizes. To identify all the 
species that may be obtained in a single haul of the 
dredge in British seas would sometimes be a hard 
task even for the most expert student of the group. 
Our present purpose, however, is not to compile a 
faunistic catalogue, but merely to give some idea of 
the endless diversity of form, and to note a few of 
the "shifts for a living" of the ways in which 
structure and habit are adapted to the conditions 
of life in the Crustacea of the shore and of shallow 
water. 

Though it might seem that the heavily armoured 
Lobsters and the larger Crabs would be sufficiently 
protected against most enemies when once they have 
attained their full size, yet they are preyed upon by 
the Octopus, which seizes them with its suckers and 
pierces their armour with its powerful beak, injecting 



go THE LIFE OF CRUSTACEA 

a poison that paralyzes its victims. Some years ago 
a " plague " of Octopus very seriously affected the 
Lobster fishery in the English Channel. To escape 
from enemies such as these, the Lobsters and many 
Crabs have the habit of lurking in crevices of the 
rocks, while in case of sudden alarm the Lobster 
may escape from danger by swimming, or rather 
darting, with great swiftness, tail foremost, through 
the water by powerful strokes of the abdomen and 
tail-fan. In the more lightly armed Prawns and 
other Crustacea of the tribe Natantia, which are 
characteristically swimmers, the power of rapid 
motion is probably the chief means of protection 
against enemies. There is reason to believe that 
the Lobsters have been derived from prawn-like 
swimming forms which have sacrificed some of their 
agility in developing their heavy armour -plating, 
retaining, however, the power of sudden and rapid 
motion in emergency. This power, again, has been 
lost by the typical Crabs (Brachyura), in which the 
abdomen is reduced in size and without a tail-fan, 
so as to be useless for swimming. While most of 
the Crabs, however, are somewhat slow of move- 
ment, trusting to their armour and their powerful 
pincers for defence, the Swimming Crabs (Portunidae 
Plate XIII.) have reacquired the power of swimming 
by means of the paddle-shaped legs of the last pair. 
Some of the tropical species of Portunidae are prob- 
ably the most expert swimmers among the Crustacea, 



CRUSTACEA OF THE SEASHORE 91 

and are described as shooting through the water like 
fish. 

The Lobster's habit of seeking shelter in rock- 
crevices or under stones is one which is shared by a 




FIG. 36 A COMMON HERMIT CRAB (Eupagurus bernhardus) REMOVED 
FROM THE SHELL 

very large number of shore Crustacea. From some 
primitive kind of Lobster which discovered the 
advantages of a portable shelter have been derived 
the Hermit Crabs. In rock-pools one may often see 
whelk or periwinkle shells tumbling about with an 



g2 THE LIFE OF CRUSTACEA 

activity quite foreign to the nature of their original 
molluscan inhabitants, and closer examination will 
show that each contains a Hermit Crab, which 
retreats into the shell when disturbed. If extracted 
from the shell, the Crab (Fig. 36) can be seen to be 
most beautifully adapted to its peculiar mode of life. 
The abdomen is soft and spirally twisted to fit into 
the interior of the spiral shell, and the uropods, 
instead of forming a tail-fan, are modified into 
holding organs, with roughened, file-like surfaces 
which can be pressed outwards against the walls of 
the shell, and wedge the body so firmly that an 
attempt to drag the animal forcibly from its retreat 
often results in tearing it in half. The front part of 
the body, which is exposed when the animal is 
walking, retains its shelly armour. One of the 
pincer-claws, most commonly the right, is much 
larger than the other, and serves to block the open- 
ing of the shell when the body is withdrawn into it. 
The next two pairs of legs are long and slender, and 
are used for walking ; but the last two pairs are 
short, with a roughened surface at the end, and 
serve to steady the body in the mouth of the shell. 
The swimmerets on the right side of the body, 
which is pressed against the central pillar of the 
shell, have disappeared, but those of the left side 
remain. 

As the Hermit grows, it is necessary for him to 
remove from time to time into a larger dwelling. 



CRUSTACEA OF THE SEASHORE 93 

It has been stated that he will sometimes dispossess 
the rightful owner of a whelk-shell for this purpose, 
dragging him out piecemeal and eating him ; but 
other observers deny that this ever happens, and in 
most cases, at all events, the Hermit is content to 
wait until he finds an empty shell of suitable size. 
After turning this over and exploring the interipr 
with his claws, to satisfy himself that it is un- 
occupied, he deftly whips the unprotected hinder 
part of his body into the new habitation, keeping 
hold of the old one meanwhile, so that he can return 
to it if the other proves unsuitable. The Hermits 
are very pugnacious, and fight with one another for 
the possession of desirable shells, the victor dragging 
his opponent out and establishing himself in his 
place. Besides appropriating the shell of a dead 
Mollusc, many Hermits seem to go into partnership 
with living animals of various kinds, and some of 
these associations will be noticed in a later chapter. 
A number of species adopt other dwellings than 
molluscan shells, and some tropical Hermits, for 
instance, are found living in the cavities of water- 
logged stems of bamboo (Fig. 37); while others, 
relinquishing the advantages of a portable shelter, 
live in holes in corals or in the canals of living 
sponges. Although in some of these cases the body 
is straight, it usually shows traces of its original 
adaptation to a spiral shell in having no swimmerets 
on the left side. 



94 



THE LIFE OF CRUSTACEA 



The only Hermits which have a full series of 
swimmerets are the primitive Pylochelidae (Fig. 37), 

which come very near 
to what we imagine 
the ancestral form of 
the group to have 
been like, and can 
hardly be separated 
from the mud-bur- 
rowing, lobster-like 
Thalassinidea. A 
few Hermits have 
given up altogether 
the use of any pro- 
tective covering. 
One of these is the 
Coconut Crab 
(Birgus), to be men- 
tioned when we come 
to deal with the Crus- 
tacea of the land. 




SYM- 

(After Another is the Stone 



FIG. 37 Pylocheles miersn, A 
METRICAL HERMIT CRAB. 
Alcock. ) ,-* i , r , i j 

Crab (L^thoaes 

The upper figure gives an end view of 

the animal lodged in a tube of water- Plate VIII.) of Our 
logged mangrove or bamboo, its , 

large claws closing the opening. wn seas, ana Its 

The lower figure shows the animal kindred, which have 
removed from its shelter. 

redeveloped shelly 

plates on the back of the abdomen, but carry it 
doubled up under the body like the true Crabs. 



CRUSTACEA OF THE SEASHORE 95 

These also preserve some traces of the original 
twisting of the abdomen, and have swimmerets only 
on one side. 

Some Crustacea construct habitations for them- 
selves. On turning over a flat stone between tide- 
marks, one often finds a little mass of bits of weed 
and rubbish attached to it, and if this be torn open 
a greenish-brown, shrimp-like animal, about three- 
quarters of an inch long, is seen slithering away on 
its side. This is an Amphipod (A mphithoe rubricata) 
which builds the shelter for itself, sticking the frag- 
ments together with threads of a cementing material 
produced by glands on the surface of its body and 
legs. Other Amphipods construct more neatly 
finished tubular dwellings of mud, or even of small 
stones, which are attached to sea-weeds and the like ; 
and some make portable shelters of the same kind, 
which they carry about with them like the caddis- 
worms of fresh-water streams. 

Some of the true Crabs also employ portable 
shields for purposes of defence or of concealment. 
The species of Dorippe which are found in tropical 
seas have the last two pairs of legs short, elevated 
on the back so that they cannot be used for walking, 
and ending in a kind of grasping claw. By means 
of these claws the Crab holds over its back some 
object, generally one valve of a molluscan shell, 
sometimes even a mangrove-leaf, to supplement the 
protection afforded by its carapace. The " Sponge 



96 THE LIFE OF CRUSTACEA 

Crabs" (Dromiidaf), of which one species, Dromia 
vulgaris (Plate IX.), occurs on the southern coasts 
of Britain, have also the last two pairs of legs 
elevated on the back and used in a similar way ; but 
in this case the covering is usually a mass of living 
sponge, one of the Sea-squirts (Tunicata), or some 
similar organism. 

Even more remarkable are the " masking " habits 
of the Spider Crabs (Oxyrhyncha). In these the 
carapace is almost always covered with sea-weeds, 
zoophytes, and other organisms which afford a very 
effective disguise. For example, specimens of the 
British species of Hyas (H. araneus and H. coarctatus) 
and Maia (M. squinado Plate XI II.) , which are very 
common on our coasts, readily escape the notice of 
the collector, as they lurk in the rock-pools. They 
are slow-moving animals, and the carapace and 
limbs are usually quite hidden by dense tufts of 
growing sea-weed, sponges, and other organisms. 
By observing the Crabs in an aquarium, it has been 
found that they actually dress themselves, plucking 
pieces of weed and the like and placing them on the 
carapace, where they are held in position by numerous 
hooked hairs. The transplanted fragments continue 
to live and grow until the Crab appears like a minia- 
ture moving forest. Still more strange is the fact 
that the Crabs appear to be able in some degree to 
adapt the nature of their covering to their surround- 
ings. It has been found that specimens dressed in 



PLATE Xlll 




A SWIMMING CRAB, Portunus dejturator. BRITISH. (REDUCED) 




A SPIDER-CRAB, Maia squinado, DRESSED IN FRAGMENTS OF WEED. 
(REDUCED) 



CRUSTACEA OF THE SEASHORE 97 

sea-weeds, when placed in an aquarium among 
sponges, picked off the weeds from their bodies and 
limbs, and planted fragments of sponge in their 
place. Not only does this habit afford the Crabs 
protective concealment, but it may also in some 
cases serve as a source of food-supply. The late 
Dr. David Robertson, of Cumbrae, one of the most 
observant of marine naturalists, saw the Crab Steno- 
rhynchus (or Macropodia) longirostris picking food- 
particles from among the vegetation on its body, and 
conveying them to its mouth. 

Many Crustacea of different orders seek conceal- 
ment and protection by burying themselves in sand. 
A pool left by the tide on a sandy beach may at first 
sight appear empty of all life, but if it be watched 
for a little while a greyish, shadowy form may often 
be seen to dart across it, to settle on the bottom 
with a little puff of sand, and to disappear. Even a 
close scrutiny of the spot will hardly discover any- 
thing, but with a hand-net one may succeed in 
scooping up, before it can dart away again, a 
specimen of the Common Shrimp (Crangon vulgaris 
see Fig. 78, p. 244), whose translucent body is 
finely mottled with greyish-brown so as to match 
exactly the sand among which it rests. 

If a spadeful of sand from between tide- marks be 

stirred up in a bucket of sea-water and allowed to 

settle for a few seconds, and the water then poured 

off through a fine muslin net, a wonderful assemblage 

7 



9 8 THE LIFE OF CRUSTACEA 

of minute Crustacea may often be obtained. Numer- 
ous species of Ostracods, Copepods, and Amphipods, 
and some Isopods, can be collected in this way, and 
some of these, at least, show peculiarities of structure 
which appear to be adapted to a sand-burrowing 
habit. Perhaps the most remarkable Crustacea 
living in such situations, however, are the Cumacea. 
In these, as already mentioned, the gills, which are 
attached to the first pair of thoracic limbs, lie one 
on each side of the thorax in a cavity enclosed by 
the carapace. These cavities are continued forwards 
to the front of the head, where they unite in a single 
opening from which a transparent tube (or a pair of 
tubes) can be protruded. It appears probable that 
this very peculiar arrangement of the respiratory 
system is adapted to enable the animals to breathe 
while buried in sand or mud. The water is probably 
drawn in behind through the narrow slit between 
the side-plates of the carapace and the bases of the 
legs, and is expelled through the tube which is 
protruded from the front of the head. In this way 
the delicate gills are protected from injury and kept 
from becoming clogged with sand, while the effete 
water, loaded with the products of respiration, is 
carried off to a safe distance, so that it does not 
re-enter the gill chamber. 

In the case of such minute forms, however, it is 
very difficult to determine the precise details of their 
mode of life by observation of the living animals. In 



CRUSTACEA OF THE SEASHORE 99 

the larger Decapods, which can be watched in their 
natural haunts, or more closely in aquaria, many 
interesting adaptations to burrowing in sand have 
been discovered. Many Crabs belonging to the tribe 
Brachyrhyncha often take refuge in sand or gravel, 
burying themselves till only the eyes remain exposed. 
The Swimming Crabs (Portunidae PlateXIII.)ofour 
own coasts have been found to use the paddle shaped 
last pair of legs for digging as well as for swimming. 
In the sand, the Crab keeps its large claws, or 
chelipeds, folded close up to the front edge of the 
carapace, which is cut into sharp, saw-like teeth. 
Between these teeth the water passes, to reach the 
entrance to the gill chamber which lies at the base of 
each cheliped, and in this way an efficient strainer is 
provided, which in coarse sand at least prevents the 
clogging of the respiratory passages. The out-going 
current of water from the gills passes through chan- 
nels that open on either side of the mouth-frame. 

A more complex adaptation of structure to the 
habit of sand-burrowing is found in the Masked Crab 
(Corystes cassivelaimus Plate XIV.). This Crab is 
common on the British coast, living in moderately 
deep water wherever the bottom is sandy, and it has 
received its English name from the fact that the 
furrows on the back of the carapace give it a grotesque 
resemblance to a human face. It is noteworthy, 
among other things, for the marked difference between 
the sexes, the male having very long, slender chelipeds, 



ioo THE LIFE OF CRUSTACEA 

while those of the female are quite short. The most 
remarkable features of its organization, however, 
have to do with its habit of burrowing in sand. The 
antennae, which in most Crabs are extremely short, 
are in this species as long as the body, and each bears 
a double fringe of stiff hairs disposed along the upper 
and under sides of the antenna, but curved inwards, so 
that when the two antennae are brought together 
parallel with each other, the hairs interlock and form 
a long tube. At its base this tube communicates 
with a space in front of the mouth, into which open 
the channels from the gill chamber at the front 
corners of the mouth-frame. The Crab burrows in 
fine sand, and the process is thus described by Pro- 
fessor Garstang : " The Crab sits upright on the 
surface of the sand; the elongated, talon-like claws 
of the four hindmost pairs of legs dig deeply into the 
sand ; the body of the Crab is thus forcibly pulled 
downwards by the grip of the legs, and the displaced 
sand is forced upwards on the ventral side of the 
body by the successive diggings and scoopings of the 
legs ; the slender chelate arms of the first thoracic 
pair assist in the process of excavation by thrusting 
outwards the sand which accumulates round the 
buccal region of the descending Crab." In this way 
the Crab descends deeper and deeper, until nothing is 
visible above the surface of the sand but the tips of 
the antennae. The antennal tube keeps open a 
channel leading from the buried Crab to the water 



PL AT EX IV 




CRUSTACEA OF THE SEASHORE 101 

above. Since this tube communicates at its base 
with the passages through which the water passes 
out from the gill chamber in most Crabs, it was 
assumed by the older observers that the antennal 
tube served to carry the outflowing water to the 
surface of the sand. It has recently been shown, 
however, by Professor Garstang that when the 
Masked Crab is buried in sand the normal respiratory 
current is reversed, water being drawn down the 
antennal tube, into the gill chambers, and passing 
out through the openings at the base of the chelipeds 
which, when the Crab is not buried, serve for its 
entrance. 

Most, if not all, of the Crabs belonging to the tribe 
Oxystomata are sand-burrowers, and the structure of 
the mouth parts characteristic of the tribe appears 
to have been acquired as an adaptation to this habit. 
As already mentioned, the mouth-frame in these 
Crabs is triangular instead of square, being produced 
forwards between the eyes, and the third maxillipeds, 
which cover it, are also elongated. In this way the" 
exhalent channels carrying the water from the gill 
chambers open on the front margin of the head, and 
are exposed even when the Crab is buried. In the 
different families of this tribe the inhalent openings 
by which the water enters the gill cavities are pro- 
tected in various ways, and so arranged that respira- 
tion can go on without danger of the gills becoming 
clogged by sediment. 



102 THE LIFE OF CRUSTACEA 

The members of the tribe Hippidea (sometimes 
called "Mole Crabs"), among the Anomura, have 
habits somewhat similar to those of the Crabs just 
described. They are common on sandy beaches in 
the warmer parts of the globe, and they burrow with 
great rapidity by means of the curved, flattened 
end-segments of the legs. The carapace is generally 
smooth and oval, and the body is compact, the short 
abdomen being folded up as in the Crabs. 

In Albunea (Plate XIV.), which belongs to this 
tribe, a long " antennal tube," which looks very like 
that of Corystes, is believed to have a similar func- 
tion in connection with respiration when the animal 
is buried. In this case, however, the tube is formed, 
not by the antennae, as in Corystes, but by the anten- 
nules, so that it affords a striking example of the 
independent evolution of similar structures from 
quite different origins. 

Hippa emerita, which is found on the coasts of 
North and South America, has the mouth parts 
imperfectly formed, and not adapted for biting ; and 
it is stated by Professor S. I. Smith that the animal 
feeds in the way that an earthworm does, swallowing 
the sand through which it burrows, and extracting 
the nutriment which it may contain. This habit, 
however, is not followed by other members of the 
tribe, for Mr. Borradaile found that a species of 
Remipes in the Maldive Islands could " easily be 
caught by a bait of Crab at the end of a line, 



CRUSTACEA OF THE SEASHORE 103 

pouncing on it with its sharp maxillipeds, and 
allowing itself to be flicked out of the sand if the 
rod be sharply lifted." 

In the cases mentioned above, the Crustacea do 
not bury themselves much below the surface of the 
sand, and do not form definite burrows ; but there 
are many Crustacea which live in open tunnels dug 
deep into the sand. Some of these belong to the 




FIG. 38 Callianassa stebbingi (FEMALE), A SAND - BURROWING 
THALASSINID FROM THE SOUTH COAST OF ENGLAND. NATURAL 
SIZE 

category of amphibious forms, to be mentioned 
presently ; but there are others which live in deeper 
water, and of which the habits are less open to 
observation. 

Nearly all the Thalassinidea (Fig. 38) live in 
burrows, often of considerable depth, in sand or 
mud. Although now classed with the Anomura, 
these animals are lobster-like in form, loosely built, 
generally with short carapace and long, soft abdomen. 



104 THE LIFE OF CRUSTACEA 

They have usually very small eyes, which appear 
as if they were not of much use for vision ; and 
some of the hinder pairs of legs are short, and 
carried folded against the sides of the body, probably 
for use when the animal is moving up or down in its 
burrow. 

Most of the Stomatopoda resemble the Thalas- 
sinidea in their mode of life, and show some curious 
similarities to them in structure, although by no 
means closely related. They are described as lying 
in wait for prey at the mouth of their burrows, 
darting out on passing fish or other animals, which 
they seize with their great saw-toothed claws, and 
retreating with great rapidity to the bottom of the 
burrow. 

Most of the Crustacea mentioned live below tide- 
marks, and at all events are rarely seen when the 
sand in which they burrow is left bare by the tide ; 
but there are others, especially on tropical shores, 
which seem to have their chief period of activity 
when the sand or mud banks on which they live are 
exposed to the air. Chief among these amphibious 
forms in the warmer seas are the Crabs of the genera 
Ocypode and Gelasimus and some of their allies. 

Some of, the species of Ocypode (Plate XV.) dig 
their burrows between tide-marks, where they are 
swamped by the advancing tide, and must be ex- 
cavated afresh when the water retreats. Other 
species, however, live above high-water mark, and 



PL A TE XV 




Ocypode cursor. WEST AFRICA. (REDUCED^ 




Gelasimus tangeri. MALE ABOVE, FEMALE HELOW. 

WEST AFRICA. (REDUCED) 



, CRUSTACEA OF THE SEASHORE 105 

are practically terrestrial animals, only entering the 
water occasionally, and, indeed, unable to survive 
prolonged immersion. The work of excavating the 
burrows has been watched in several species. The 
Crab comes out of the burrow sideways, carrying a 
load of sand between two of the walking legs on the 
rear side. By a sudden movement the sand is jerked 
away to some distance, where it accumulates in a 
little heap, and the Crab dives into the burrow for 
another load. Most of the Crabs belonging to this 
genus possess a curious " stridulating organ " on one 
of the large claws, by means of which they can 
produce a buzzing or hissing sound. On the inner 
surface of the "hand" there is a raised patch, 
which, when examined with a lens, is seen to be 
made up of a series of fine ridges, like the teeth of 
a file. When the limb is bent in towards the body, 
this patch can be rubbed up and down against a 
sharp-edged ridge or scraper on the third segment of 
the limb, and in this way the sound is produced. 
What the use of the sound may be is not quite clear, 
but there is probability in Dr. Alcock's suggestion 
that it serves to warn intruders that the burrow is 
already occupied. These Crabs run very swiftly, and 
one species was seen by Professor S. I. Smith to 
catch Sand-hoppers (Amphipods of the family Tali- 
tridse) by springing on them suddenly, " very much 
as a cat catches mice," but it also fed on dead fish 
and the like. 



106 THE LIFE OF CRUSTACEA 

Of somewhat similar habits are the numerous 
species of the genus Gelasimus (" Fiddler Crabs " 
Plate XV.), which abound on sand and mud flats of 
tropical shores. These little Crabs are remarkable 
for the great dissimilarity between the sexes in the 
form of the chelipeds. In the female both chelipeds 
are small and feeble, but in the males one of them, 
either the right or the left, is enormously enlarged, 
sometimes exceeding in length and breadth the body 
of the Crab which carries it. What the precise use 
of this enormous claw may be does not seem to be 
quite certainly known. It is said to be used as a 
weapon by the males in fighting with one another, 
but it seems too clumsy to be very efficient for this 
purpose. It is often brilliantly coloured, and has 
been supposed to be a sexual adornment. 

In Ocypode and Gelasimus the respiratory apparatus 
is modified for the purpose of breathing air. The 
gills are similar to those of purely aquatic Crabs, and 
no doubt serve for respiration when the animal is in 
the water; but the gill chambers are much more 
spacious than usual, and the lining membrane is 
richly supplied with bloodvessels. Air is admitted 
to the gill chambers by an opening, protected by a 
brush of hairs, between the second and third pairs of 
walking legs on each side. It is believed that in 
this way the gill chamber is fitted to be used as a 
lung when the animals are out of the water. Similar 
arrangements in some of the more exclusively 



CRUSTACEA OF THE SEASHORE 107 

terrestrial Crustacea will be mentioned in a later 
chapter. 

There are many Shore Crabs, however, which lead 
a more or less amphibious existence without showing 
any marked modifications of structure as compared 
with their more purely aquatic relatives. On our 
own coasts, the Common Shore Crab (Carcinus 
m&nas Plate IX.) commonly spends several hours 
each day exposed to the air, and in an aquarium it 
will voluntarily leave the water if the opportunity be 
afforded it. On tropical coasts the species of Grapsus 
and allied genera are often seen clambering with 
great agility about exposed rocks. 

Analogous habits to those of the sand-burrowing, 
amphibious Crabs described above are shown on a 
small scale by the Amphipods of the family Tali- 
tridae, known as " Sand-hoppers " or " Beach-fleas." 
Everyone who has walked over the firm sand near 
high-water mark on our own shores must have 
noticed the myriads of actively hopping little crea- 
tures disturbed at every step. The commonest 
species of Sand-hopper on the British coasts is 
Talitrus saltator (Fig. 39), but Orchestia gammarellus 
is also common. Both species occur together on 
sandy beaches or among decaying sea-weeds, and 
are among the most important scavengers of the 
seashore, picking clean the bones of fish or other 
animals cast up by the tide. In this country the 
Sand-hoppers do not, as a rule, venture far above 



io8 THE LIFE OF CRUSTACEA 

high-water mark ; but in warmer climates species of 
Talitridse live in the damp forests at great distances 
from the sea, and deserve to be ranked among the 
terrestrial Crustacea. 

It has been mentioned above that the Common 
Shrimp is protected, not only by its habit of lying 
half buried in sand, but also by its close resemblance 
in colour to the sand among which it lives. There 




FIG. 39 THE COMMON SAND-HOPPER (Talitrus saltator), MALE, 
FROM THE SIDE, x 3. (After Sars.) 



are many others among the shore Crustacea which 
show what seems to be a " protective resemblance " 
in colour and form to their surroundings. It is 
necessary to be cautious in interpreting these re- 
semblances as necessarily protective, since the fish 
and other enemies which prey on these Crustacea 
see them with eyes very different from ours, and 
probably, in many cases, are guided to their prey by 
the sense of smell rather than by sight. The 
" masking " habit of the Spider Crabs, already 



CRUSTACEA OF THE SEASHORE 109 

described, strongly suggests, however, that conceal- 
ment from sight is an important protection to some 
shore Crustacea, and helps to make it probable that 
the same end is reached in other cases by modifica- 
tions of form and colour. 

There can be no doubt, at all events, that many 
Crustacea are very inconspicuous to human eyes 
when they remain motionless in their natural sur- 
roundings. Thus, for example, the Caprellidae, or 
" Skeleton Shrimps " (see Fig. 22, p. 54), are hard to 
detect without very close search, as they cling to the 
feathery branches of the hydroid zoophytes among 
which they are usually found. They are strangely 
modified Amphipods, in which the body is slender 
and thread-like, and generally of a semi-transparent, 
whitish or yellowish colour, like the zoophytes on 
which they live. They clamber about among the 
branches with a movement like that of a " looper " 
caterpillar, and often remain clinging by means of 
the hooked claws of the hinder pairs of legs, with 
the fore part of the body gently waving about. 

The little Crabs of the family Leucosiidse (Oxy- 
stomata), of which the British representatives are 
several species of the genus Ebalia, are often ex- 
tremely like pebbles of the gravel among which they 
live. In many tropical species the carapace is pitted 
and eroded, so as to resemble a worn fragment of 
coral shingle. One of the most striking cases among 
the Crabs, however, is that of Huenia proteus 



no 



THE LIFE OF CRUSTACEA 



(Fig. 40), one of the Spider Crabs (Oxyrhyncha), 
which is found in the Indian and Pacific Oceans. 
In this little Crab the carapace is flat, and is extra- 
ordinarily variable in form. In most of the males it 

is triangular in outline, but 
in most of the females and 
in some males it is broadened 
by leaf-like expansions of the 
side edges. Borradaile has 
pointed out that these broad 
individuals are usually found 
among the sea-weed Hali- 
meda, and that they closely 
resemble the fronds of this 
weed in form and in their 
greenish colour. 

A nnmhpr nf Prnctsirpa arp 
A n 

known to possess a chame- 




FIG. 40 A, A PIECE OF A 

TROPICAL SEA-WEED 
(Halimeda) ; B, A CRAB 
(Huenia proteus) WHICH 

LIVES AMONG THE 

FRONDS OF Halimeda, AND leon-llke power of changing 

CLOSELY RESEMBLES THEM J , , , , 

IN FORM AND COLOUR, their colour. The mechanism 
REDUCED. (After Borra- b which th j s change is ef- 
daile.) * 

fected is similar to that found 

in other animals, such as fish and frogs, which have 
the same power. The pigment which gives its colour 
to the animal is lodged in microscopic star-shaped 
bodies known as chromatophores, lying for the most 
part just below the skin. Each chromatophore 
consists of a central body from which a number of 
branching filaments radiate. The pigment may con- 



CRUSTACEA OF THE SEASHORE in 

tract into the centre of the chromatophore, forming 
a minute and hardly visible speck, or it may spread 
out into the branching filaments, forming a distinct 
spot of colour. Each chromatophore may in some 
cases contain several colours of pigment, and these 
may expand or contract independently of each other, 
so that a whole series of changes may be produced by 
a single chromatophore. In the larger Crabs and 
Lobsters the visible colour of the animals depends 
on pigment in the shelly exoskeleton, which is thick 
enough to hide the chromatophores in the living 
tissues underneath, and no very rapid or considerable 
changes are apparent ; but in the smaller forms, in 
which the exoskeleton is thin and translucent enough 
to allow the underlying colours to appear through it, 
the changes in the chromatophores may produce 
striking effects. Thus, Fritz Miiller describes a 
species of Fiddler Crab of the genus Gelasimus, in 
which the hinder part of the carapace was brilliantly 
white, but five minutes after the Crab was cap- 
tured it had changed to a dull grey. Many other 
cases of colour change have been described, but 
most remarkable and the most fully studied is that 
of the Prawn, Hippolyte varians, which is very 
common on our own coasts, and has recently been 
the subject of a very elaborate series of researches by 
Professors Keeble and Gamble. The specimens of 
this Prawn show " a bewildering variety of colour 
and of colour-pattern"; they may be uniformly 



ii2 THE LIFE OF CRUSTACEA 

coloured in various shades of brown, green, or red, 
or they may be " blotched," "barred," or "lined," 
with colour. These different varieties are generally 
found among sea-weeds, which they resemble in 
colour and pattern, the " lined " forms, for instance, 
frequenting finely branched and feathery weed. Like 
many other protectively coloured animals, they are 
of sedentary habits, clinging to the weed, and seldom 
moving by day. If a specimen be removed from its 
habitat and placed in an aquarium with different 
kinds of sea-weed, it will take refuge among that 
which it most closely resembles. It appears that 
this resemblance in colour-pattern is acquired during 
the growth of the Prawn, and that a young specimen 
kept among finely branched sea-weed will acquire the 
"lined " pattern, while others, living among coarser 
weed, become " barred," " blotched," or " mono- 
chrome." Even in the adult Prawns the colour 
(though not the pattern) becomes changed in a day 
or two if they are placed among weed of a different 
colour from green to brown, or the like. Within 
certain limits still more rapid changes of colour take 
place. If kept in the dark, or if placed on a white 
background (for example, in a porcelain dish) in the 
light, the Prawn quickly becomes nearly colourless, 
by contraction of the chromatophores, a transparent 
bluish tint alone remaining, due to a substance which 
diffuses from the chromatophores into the fluids of 
the body. In natural conditions this phase is assumed 



CRUSTACEA OF THE SEASHORE 113 

at night ; and the interesting observation has been 
made that Prawns kept in the dark continue for 
three or four days to show a periodic expansion and 
contraction of the chromatophores, corresponding 
to the alternation of day and night. It seems that 
the rhythm of light and darkness has become im- 
pressed on the chromatophore system of the. animal, 




FIG. 41 THE COMMON PORCELAIN CRAB (Porcellana longicornis), 
SLIGHTLY ENLARGED, AND ONE OF THE THIRD MAXILLIPEDS 
DETACHED AND FURTHER ENLARGED TO SHOW THE FRINGE OF 
LONG HAIRS 



and the movement of the pigments is regulated by 
something analogous to memory. 

It has already been mentioned, in dealing with the 
Lobster, that certain Crustacea have the power of 
voluntarily throwing off some of their limbs (auto- 
tomy). In many cases, as in the Lobster, this power 
is mainly of use in enabling the animal to discard an 
injured limb ; but there are some Crustacea which 
seem to adopt it as a means of escaping from the 
attack of an enemy. On our own coasts the shore 
8 



H4 T HE LIFE OF CRUSTACEA 

collector will, often find, on turning over a large 
stone, one or more specimens of the little Porcelain 
Crabs (Porcellanaplatycheles, or P. longicornis Fig. 41) 
clinging to its under-side. If these Crabs be seized 
by one of the large claws, they frequently leave the 
claw in the captor's hand and scuttle off without it ; 
and it cannot be doubted that, as in the case of 
lizards and other animals which have a similar power 
of self-mutilation, this habit often enables them to 
escape from their natural enemies. 

Although the Crustacea as a whole are pre- 
dominantly active animals, many examples have 
already been mentioned of species which are more 
or less sluggish and sedentary in their habits. The 
extreme degree of passivity is reached by the 
Barnacles (Cirripedia), which differ from all other 
Crustacea (except some parasites) in being fixed to 
one spot, and quite without the power of locomotion 
in the adult state. Most of the Barnacles met with 
on the shore or in shallow water belong to the 
division of the Sessile Barnacles or Acorn-shells 
(Operculata). Every visitor to the seashore has 
noticed the little conical shells which cover exposed 
rocks as if with a coat of rough-cast. On the 
British coasts the commonest species is Balanus 
balanoides (Plate III.), though other species closely 
resembling it are also common. They are to be 
found almost up to high-water mark in situations 
where they are left uncovered for many hours every 



CRUSTACEA OF THE SEASHORE 115 

day ; but the valves which close the opening of the 
shell fit so tightly that a little sea-water is enclosed, 
and the animal is protected from drying up even when 
exposed to the heat of the sun. If a stone or a chip 
of rock, with a few of these animals on it, be placed 
in a jar of sea-water, their peculiar mode of obtaining 
food can easily be watched. The valves will presently 
be seen to open a little, and the curled cirri will be 
protruded, opened out like the fingers of a hand, 
and withdrawn again with a sort of grasping motion. 
These movements are continued without stopping 
while the animal is under water. If the cirri be 
examined with a pocket-lens or under a microscope, 
it will be seen that they are fringed with stiff bristles, 
so that, when they are opened out, the whole forms 
a kind of " casting-net." As it is swept through the 
water, this net entangles minute floating particles of 
animal or vegetable matter, and carries them into 
the shell, so that they can be seized by the jaws and 
swallowed. The cirri, as we have already seen, are 
really the modified thoracic limbs, so that, in Huxley's 
words, " A Barnacle may be said to be a Crustacean 
fixed by its head, and kicking the food into its 
mouth with its legs." 

A mode of obtaining food by " net-fishing," not 
unlike that employed by the Barnacles, is found in 
certain Crustacea belonging to a widely different 
group the little "Porcelain Crabs" (Fig. 41) 
mentioned above. Mr. Gosse observed that the 



n6 THE LIFE OF CRUSTACEA 

Broad-clawed Porcelain Crab (Porcellana platychelcs] 
employed its third pair of maxillipeds, which are 
thickly fringed with long feathered hairs, in making 
alternate casting movements " exactly in the manner 
of the fringed hand of a Barnacle, of which both the 
organ and the action strongly reminded me." 



CHAPTER VI 
CRUSTACEA OF THE DEEP SEA 

IT has already been mentioned that the animals 
living on the sea-bottom in shallow water do not 
differ greatly in character from those that may be 
found between tide-marks. As we go farther out 
from land, however, into the deeper water, the 
character of the fauna gradually changes. One by 
one the species found near the shore become rare 
and disappear, and their places are taken by others 
characteristic of the intermediate depths. These in 
their turn give way to others, till in the abysses of 
the great oceans we find an assemblage of strange 
animals adapted to the conditions of life in the great 
depths, and differing widely in many respects from 
the more familiar inhabitants of the coastal waters. 
In this " fauna of the deep sea," which extends to 
the greatest depths reached by the dredge or trawl, 
the Crustacea occupy a prominent place. Before pro- 
ceeding to discuss some of these peculiar forms, 
however, it is necessary to attempt to form some 
idea of the conditions under which they live. 

117 



n8 THE LIFE OF CRUSTACEA 

In the first place, the character of the sea-bottom 
changes very greatly as we pass away from the 
coast. Near the shore it is extremely diversified, 
consisting in one place of rocks swept bare by the 
tides or overgrown with jungles of sea-weed, in 
another of banks of gravel or shingle, of sand or of 
mud, but in all cases derived from the "waste" of 
the land, as it is eaten away by the waves or washed 
down by the rivers. As the distance from land 
increases, the deposits become finer and finer, till 
they shade off into a soft oozy mud, composed of 
the finest particles brought down by the rivers. In 
the neighbourhood of large rivers this mud may 
sometimes extend for hundreds of miles from the 
land, but there is a limit to the distance to which 
even the finest particles can drift before they settle 
to the bottom, and beyond this limit the floor of the 
ocean is covered by sediments which owe their 
origin, not to the land, but to the ocean itself. The 
surface waters of the ocean everywhere teem with a 
vast variety of floating animals and plants, and, as 
these die, their remains sink to the bottom " like a 
perpetual shower of rain." 

Among the most abundant floating organisms 
in the warmer seas, at any rate are certain minute 
animals known as Foraminifera, which belong to 
the lowest class of the animal kingdom, and 
have shells composed, in most cases, of carbonate 
of lime. Over vast areas the bottom of the ocean 



CRUSTACEA OF THE DEEP SEA 119 

is covered with a soft grey ooze, made up almost 
entirely of the dead shells of Foraminifera rained 
down from above. Since the commonest species 
of Foraminifera found under these circumstances 
belong to the genus Globigerina, the deposit is 
known as " Globigerina ooze." 

In certain regions of the ocean the shells of other 
floating organisms largely replace those of the 
Foraminifera in covering the ocean floor, and in 
the deepest abysses so deep that the shells of 
surface animals are dissolved before they can sink 
to the bottom there is found a deposit known as 
the " red clay," which appears to be derived largely 
from the impalpable volcanic and cosmic dust that 
floats in the atmosphere. It is not necessary for 
our present purpose to enter more fully into the 
interesting questions connected with these deep-sea 
deposits, but it is important to remember that, 
generally speaking, the floor of the deep sea is 
everywhere soft ooze, without rocks or stones, 
except for an occasional water-logged lump of pumice 
or a stone dropped by a melting iceberg. This fact 
is probably of great importance in the life of deep- 
sea animals. 

One of the most peculiar and characteristic of the 
physical conditions in the deep sea is the enormous 
pressure under which life has to be carried on. At 
the surface of the sea the pressure of the atmosphere 
is, roughly speaking, 14! pounds per square inch. 



120 THE LIFE OF CRUSTACEA 

At a depth of only 33 feet of water this pressure is 
doubled, and at greater depths the pressure increases 
in proportion, till at 2,000 fathoms it is more than 
2.\ tons on the square inch. As a matter of fact, 
however, the animals at the bottom of the sea are 
probably but little affected by this enormous pressure. 
Only, when they are brought up by the dredge the 
sudden release of pressure causes the fluids of the 
body to expand and destroys the tissues, so that the 
animals are generally dead or dying when they reach 
the surface. 

More important than the pressure in its influence 
on life is the darkness of the depths. The light of 
the sun only penetrates the water of the sea to a 
comparatively small depth. At 200 fathoms there 
is not enough light to produce any effect on a photo- 
graphic plate. Even at a considerably less depth 
the absence of light puts an end to all plant-life, 
except for the ubiquitous bacteria, and it follows 
that all the animals of the deep sea ultimately depend 
for their food-supply on the rain of dead bodies of 
surface animals which, as already mentioned, is con- 
stantly falling on the sea-bottom. 

The temperature at the bottom of the deep sea is 
always very low. Dr. Alcock states that " in the 
open part of the Bay of Bengal, where the mean 
surface temperature is about 80 F., the temperature 
at a depth of 100 fathoms is only about 60 F., at 
a depth of 300 fathoms not quite 50 F. ; while at a 



CRUSTACEA OF THE DEEP SEA 121 

depth of 2,000 fathoms the temperature all the year 
round is only 3 above freezing-point." 

Finally, it is important to notice the uniformity of 
the conditions at the bottom of the sea ; not only 
are the alternation of night and day and the progress 
of the seasons unfelt in the abysses, but the con- 
ditions are practically the same over vast areas in all 
the oceans. 

In the case of deep-sea Crustacea, we are fre- 
quently confronted with a difficulty which does not 
occur in the case of some other groups of animals 
Corals or Echinoderms, for example the difficulty, 
namely, of deciding whether the animals really lived 
on or near the bottom, or were captured by the open 
mouth of the trawl on its way to the surface. When 
the animals are plainly not well adapted for swim- 
ming as, for instance, most of the Crabs. it may 
be assumed that they did actually live on the 
bottom ; but, with the prawn-like forms, the possi- 
bility that they may really be inhabitants of the 
intermediate depths must always be taken into 
consideration. 

In animals that live in perpetual darkness we 
should expect to find, in accordance with the prin- 
ciple of adaptation which runs through the whole 
of organic nature, that the eyes are wanting or 
imperfectly developed. In a great many deep-sea 
animals this is indeed the case. The deep-sea 
Lobsters of the genus Nephropsis (Fig. 42), which 



122 



THE LIFE OF CRUSTACEA 



are very closely allied to the Norway Lobster 
(Nephrops) of shallow water, have very short and 
slender eye-stalks hidden under the rostrum, and 
showing at the tip only the merest traces of what 




FIG. 42 A DEEP-SEA LOBSTER (Nephropsis stewartii), FROM THE 
BAY OF BENGAL. REDUCED. (After Alcock and Anderson.) 

was once an eye. In the lobster-like Eryonidea 
(see Fig. 46, p. 133), the reduced eye-stalks are firmly 
fixed in notches in the front edge of the carapace. 
Some of the deep-sea Crabs and Prawns seem also 
to be totally blind. In a great many cases degenera- 



CRUSTACEA OF THE DEEP SEA 123 

tion has not quite gone so far, and the eyes are 
present, although much reduced and modified. Thus, 




FIG. 43 Munidopsis regia, A DEEP-SEA GALATHEID FROM THE BAY 
OF BENGAL. REDUCED. (After Alcock and Anderson.) 

the very numerous deep-sea species of Galatheidae, 
belonging to the genus Munidopsis (Fig. 43) and its 



124 THE LIFE OF CRUSTACEA 

allies have, as Alcock says, " pallid, milky-yellow, 
lack-lustre eyes which, though they may perhaps 
serve to distinguish between light and darkness, can 
never form a definite visual image." It is probable, 
indeed, that these pale-coloured eyes are specially 
adapted for vision in a dim light, for it has been 
shown that in certain deep-sea Euphausiacea the 
pigment-sheaths between the separate elements of 
the compound eyes are greatly reduced, and are 
fixed in the position temporarily assumed by those 
in the eyes of normal Crustacea when kept in the 
dark. Be this as it may, there are many deep-sea 
Crustacea which have well-developed and darkly- 
pigmented eyes. Some of these are swimming forms, 
which may at times migrate into the upper strata 
of water to which some rays of light penetrate ; but 
there are some cases of Crabs and other bottom- 
living species that have well-developed eyes, although 
they live at great depths. This would seem to sug- 
gest that, although shut off from the light of day, 
they are not condemned to grope in perpetual dark- 
ness. Many deep-sea animals are known to be 
phosphorescent, and it seems probable that the 
large-eyed species may profit by the light emitted 
by the glow-worms and fireflies of the abyss. Thus, 
Alcock points out that the deep-sea Hermit Crab 
Parapagurus pilosimanus (Plate XVI.), which lives in 
partnership with a colony of sea-anemones which it 
carries about with it, has large eyes, although it 



PLATE XVI 




A DEEI'-SEA HERMIT-CRAB, t'araptigurus pilosiiitamts, 
SHELTERED BY A COLONY OF EftizoantllUS. FROM 

DEEI' WATER OFF THE WEST OF IRELAND 
(SLIGHTLY REDUCED) 



CRUSTACEA OF THE DEEP SEA 125 

descends to depths of at least 2,000 fathoms ; and 
he suggests that the Crab may be able to see its way 
by the light emitted by the zoophytes. 

Some of the Crustacea, however, are themselves 
luminous. Thus, Alcock records how specimens of a 
deep-sea Prawn, Heterocarpus alphonsi, "poured out, 
apparently from the orifices of the ' green glands ' at 
the base of the antennae, copious clouds of a ghostly 
blue light of sufficient intensity to illuminate a bucket 
of sea-water so that all its contents were visible in 
the clearest detail." Certain other Prawns are 
known to possess special light-producing organs on 
various parts of the body and limbs. It is in the 
Euphausiacea, however, that these organs have been 
most fully examined, and although the members of 
this group (see Fig. 24, p. 56) are by no means all 
deep-sea animals, some of them occurring at the 
surface of the sea, the structure of their luminous 
organs, or " photophores," may appropriately be 
described here. They are situated on the under- 
surface of the abdomen, in the basal segments of 
some of the thoracic legs, and on the upper surface 
of the eye-stalks. Each consists of a globular cap- 
sule covered by a layer of pigment, except on the 
outer side, where there is a transparent biconvex 
lens. In the centre of the capsule is a peculiar 
" striated body " which seems to be the actual seat 
of luminescence, and behind it is a concave reflector 
composed of concentric lamellae, and having a silvery 



126 THE LIFE OF CRUSTACEA 

lustre. Before their luminosity was observed, these 
organs were described as " accessory eyes," but there 
can be little doubt that they serve rather as search- 
lights, although, from the positions that some of 
them occupy on the body, it is not easy to see how 
they can illuminate objects within range of the eyes. 
That the function of phosphorescent organs is not 
always that of giving light for their possessor to see 
by is shown by the fact that many luminous animals 
are blind. It is important to notice, however, that 
these blind animals never have complex "photo- 
phores" like those just described, but only exhibit 
a diffuse luminosity or give off luminous secretions ; 
as an example among Crustacea, the blind Eryonidea 
(see Fig. 46, p. 133) may be mentioned, one species of 
which was observed by Alcock to be " luminous at 
two points between the last pair of thoracic legs, 
where there is a triangular glandular patch." In a 
recent discussion of the whole question of phos- 
phorescence in marine organisms, Dr. Doflein con- 
cludes that the part it plays in the life of the 
animal probably differs in the different cases. In 
some it may serve to attract prey, as moths are 
attracted to a candle ; in others it may help 
individuals of the same species to keep together 
in a swarm or to find their mates, the varying 
arrangement of the photophores producing character- 
istic light-patterns that serve as " recognition marks " 
like the colour-patterns of animals that live in the 



CRUSTACEA OF THE DEEP SEA 127 

light of day. The clouds of luminous secretion thrown 
out by Heterocarpus and other Prawns, and by certain 
Mysidacea and Ostracods, may serve to baffle 
pursuers, like the cloud of ink thrown out by a 
Cuttlefish, and in some cases the more complex 
organs may illuminate objects within the range of 
vision. That this does not exhaust the possibilities 
of speculation on the subject, however, is shown by 
the case of certain deep-sea Prawns which have 
been recently discovered to possess photophores 
placed so as to illuminate the interior of the gill 
cavities. What function they can discharge in this 
position seems beyond conjecture. 

The colours of deep-sea Crustacea are very curious. 
Few of them have the blanched appearance common, 
for instance, in animals that live in the darkness of 
caves ; on the contrary, their colours are often very 
vivid, but they are nearly always uniform, without 
spots or markings, and in a large proportion of cases 
are in some shade of red or orange. This red colour 
seems to be associated, in some way that we do not 
understand, with the darkness of their habitat. The 
general absence of markings is very striking. Dr. 
Alcock remarks that in deep-sea Crustacea we never 
see "those freaks of colour, or those labyrinthine 
mottlings and dapplings, that excite our curiosity 
when handling the Crabs and Shrimps of the reefs." 
Possibly the explanation of this may be that in these 
dwellers in darkness colour is merely, as it were, an 



128 THE LIFE OF CRUSTACEA 

accident, a by-product of physiological processes 
directed to other ends, not a character of protective 
or warning value, as in animals that hunt and are 
hunted in the light of day. It is a curious fact, 
which may have some bearing on this problem, that 
in many cases, while the adults are coloured in some 
shade of red, the eggs carried by the female are 
bright blue or green. 

Some of the peculiarities of structure observed in 
deep-sea Crustacea seem to be correlated with the 
difficulties of resting or moving about with security 
on the soft ooze of the sea-floor. Among the Crabs 
we find a preponderance of long-legged species, not 
only among the true Spider Crabs (Oxyrhyncha), but 
also in other groups (Dromiacea like Latreillia, 
figured on Plate XIX., and Oxystomata), the 
members of which assume the same spider-like form. 
In some cases the legs are fringed with long stiff 
hairs, which may help to prevent the animal from 
sinking in the ooze, and the spines on the body and 
legs of many species may have the same effect. 
Among the deep-sea Prawns, the species of the 
family Nematocarcinidae (Plate XVII.) have ex- 
tremely long and slender legs, which we may assume 
to be used like stilts for walking over the soft ooze. 

Not much is known regarding the food of deep- 
sea animals. In the absence of plant-life they must 
of necessity be all carnivorous, and all ultimately 
dependent on the food-supply falling from above. 







PLATE XVII 




II 



CRUSTACEA OF THE DEEP SEA 129 

Some species have been found to have the food- 
canal filled with Globigerina ooze, which they no 
doubt swallow, as earth-worms do the soil in which 
they burrow, for the purpose of extracting the nutri- 
ment that it contains. In one species of deep-sea 




FIG. 44 Thaumastocheles zaleucus. REDUCED. (After Spenoe Bate.) 

Cumacea (Platycuma holtt), which appears to feed in 
this manner, the food-canal is coiled, a condition 
very rare in Crustacea ; in all probability this is due 
to the necessity for an increase of the absorptive 
surface, since it is common to find such an increase, 
either by lengthening and consequent coiling of the 
9 






130 THE LIFE OF CRUSTACEA 

gut, or by infolding of its walls, in animals that have 
to swallow large quantities of relatively innutritious 
food material. Many species, however, no doubt 
have more selective habits of feeding. The lobster- 
like Thaumastocheles (Fig. 44), which was dredged by 
the Challenger expedition in the West Indies at a 
depth of 450 fathoms, and has since been got from 
deep water off the Japanese coast, has one of the 
chelae enormously enlarged, with long and slender 
fingers set with spines like the teeth of a rake. It 
has been suggested that this remarkable claw may 
be used for raking or sifting the ooze for small 
animals on which the Thaumastocheles feeds. A 
similar function may be suggested for the long and 
spiny first pair of walking legs in the Spider Crab 
Platymaia (Fig. 45). 

In many deep-sea Crustacea the eggs are of very 
large size, indicating that the young are hatched in 
an advanced stage of development. For example, 
in the numerous species of the genus Munidopsis the 
eggs are always large and correspondingly few in 
number, in striking contrast to the closely allied 
genus Galathea, from shallow water, in which the 
eggs are small and very numerous. Alcock mentions 
that a deep-sea Prawn of the genus Psathyrocaris, 
although only about 3^ inches long, has eggs nearly 
a quarter of an inch in length. It would seem that, 
in some way or other, the conditions are unfavour- 
able for a free-swimming larval life ; but they cannot 



PLATE XVIII 




Bathynomus giganteus, ABOUT ONE-HALF NATURAL SIZE 

(From Lull/tester's " Treatise on Zoology" after Milne-Edwards 
an.i Bou-vter) 



CRUSTACEA OF THE DEEP SEA 131 

be altogether prohibitive, for there are a good many 
characteristically deep-sea Crustacea, such as the 
Eryonidea, that have small eggs and presumably a 
larval metamorphosis. 

The uniformity of the physical conditions over 
vast areas in the deep sea is no doubt the cause of 
the enormously wide geographical range of many 




FIG. 45 A DEEP-SEA CRAB (Platymaia wyville-thomsoni). REDUCED. 
(After Miers.) 

species of deep-sea animals. There are many 
examples of this among Crustacea, and they are 
added to by every deep-sea dredging expedition. 
For example, the giant Isopod Bathynomus 
(Plate XVIII.) was first discovered in West Indian 
seas, and the same species has since been dredged 
near Ceylon, while a second species has been found 
off the Japanese coast. Of the strange lobster-like 






132 THE LIFE OF CRUSTACEA 

Thaumastocheles (Fig. 44), mentioned above, only 
four specimens are known one dredged by the 
Challenger in the West Indies, and three others 
more recently brought from Japan. 

The low temperatures prevailing in deep water, 
even in tropical seas, render it possible for many 
Crustacea to live there which are closely allied to, 
or identical with, species occurring in shallow water 
in the colder seas of the North and South. Many 
examples of this are mentioned by Dr. Alcock in his 
discussion of the deep-sea fauna of Indian seas ; for 
example, the Lobster Nephrops andamanicus, found at 
depths of 150 to 400 fathoms in the Indian seas, is 
very closely allied to the Norway Lobster (Nephrops 
norvegicus) of our own coasts. To some extent this 
fact affords an explanation of the phenomenon that 
has been called " bipolarity " in the distribution of 
marine animals. It has been observed that certain 
families, genera, and even species, are found in the 
Arctic and Antarctic seas, although they seem to be 
entirely absent from the intervening tropical zones. 
In some cases, however, it has been found that these 
forms occur in the deep sea in the warmer regions 
where the cold water offers them a connection 
between North and South without any great differ- 
ence of temperature. 

In the early days of deep-sea exploration, when 
naturalists were becoming aware of the rich fauna 
inhabiting the abysses of the ocean, which till then 



CRUSTACEA OF THE DEEP SEA 133 



had been supposed to be barren of all life, it was 
confidently expected that representatives would be 
discovered of some of the 
animals known as fossils 
from the earlier geological 
periods. It was believed 
that the great ocean basins 
had remained unchanged 
for vast periods of geologi- 
cal time, and that numer- 
ous "living fossils" would 
be found surviving in the 
depths. These hopes have 
not been fully realized, for 
the deep-sea fauna as a 
whole has proved to be of 
a comparatively modern 
type ; nevertheless, it does 
include a considerable 
number of primitive and 
old-fashioned forms of life, 
some of which belong to 
groups elsewhere extinct. 
This is conspicuously the 

,1 /-. FIG. 46 Polycheles phosphorus, 

case among the Crustacea. ONE OF THE ERYONIDEA, 

The lobster-like Eryonidea, ^MALE FR ."? J NDIAN 

* SEAS. (From British Museum 

which at the present day Guide, after Alcock.) 

are only found in the deep sea, were long known as 

fossils before they were discovered to survive as living 




134 THE LIFE OF CRUSTACEA 

animals. The existing species (Fig. 46) are all blind, 
with only vestiges of eye-stalks, and they may be 
readily distinguished by the fact that the first four, and 
sometimes all five, pairs of legs end in chelae, no other 
Decapods having more than three pairs of chelate 
legs. The fossils occur in rocks of the Secondary 
Period, from the Trias to the early Cretaceous. 
Some of them, at least, had well-developed eyes, and 
probably lived in shallow water. This was almost 
certainly the habitat of those (Fig. 47) that are found 
preserved in a marvellously perfect state in the litho- 
graphic limestone of Solenhofen (famous for the 
discovery of Arch&opteryx and many other remark- 
able fossils), which is believed to have been deposited 
in a lagoon. After the early part of the Cretaceous 
epoch, the Eryonidea are no longer found as fossils, 
and it is, at all events, a probable conjecture that 
about that period they forsook the shallow waters 
for the deeper recesses of the ocean, where their 
descendants have held their own till the present day. 
Another group of deep-sea Crustacea which has 
affinities with certain fossil forms is the little family 
Homolodromiidae among the Crabs. It has already 
been mentioned that the Dromiacea are the most 
primitive tribe of the Brachyura, and Professor 
Bouvier has shown that among these the Homolo- 
dromiidae approach most nearly to the lobster-like 
forms from which the Crabs have been derived. He 
has further shown that the members of this family 



CRUSTACEA OF THE DEEP SEA 135 

closely resemble in the arrangement of the grooves 
upon the carapace the extinct Prosoponidae, which 




FIG. 47 Eryon propinquus, ONE OF THE FOSSIL ERYONIDEA, FROM 
THE JURASSIC ROCKS OF SOLENHOFEN. (From Lankester's 
" Treatise on Zoology," after Oppel.) 

are known as fossils from Jurassic and Cretaceous 
rocks. 



136 THE LIFE OF CRUSTACEA 

It is in the deep sea also that we find the curious 
Hermit Crabs of the family Pylochelidcz (Fig. 37, p. 94), 
which are perfectly symmetrical and show no trace 
of having ever adopted the habit of living in Gastro- 
pod shells ; so primitive, indeed, are these forms that 
it is not easy to find characters by which to define 
them from the lobster-like Thalassinidea or from the 
true Lobsters themselves, and, although no fossil 
representatives are yet known, there seems no reason 
to doubt that the Pylochelidae are nearly related to 
the primitive stock from which the other Hermit 
Crabs have been evolved. Among the deep-sea 
Prawns there are many forms, both of Penseidea and 
of Caridea, which are more primitive than most of 
their relatives from shallow water ; and although in 
these cases also the geological records are faulty, we 
may assume, if we cannot prove in detail, a general 
similarity to the fossil Prawns of Mesozoic rocks. 

When all has been said, however, perhaps the most 
surprising thing about the deep-sea fauna is, not that 
the animals are unlike those living in shallow water, 
but that they differ from them so little. When we 
consider the physical conditions of the oceanic 
abysses the absolute darkness, the freezing cold, 
the pressure measured in tons on the square inch 
it would seem inevitable that the physiological pro- 
cesses of deep-sea animals must differ greatly from 
those of animals living in shallow water ; yet in 
very many cases these differences of function are 



CRUSTACEA OF THE DEEP SEA 137 

accompanied only by the most trivial differences 
in structure. To take one example, the " Pink 
Shrimp" (Pandalus montagui), which we may find 
commonly between tide-marks on our own coasts, 
differs only in inconspicuous details from species of 
the same genus living at a depth of 600 fathoms ; 
while other genera of the family Pandalidae range 
downwards to 2,000 fathoms or more, without any 
important divergences in structure. 



CHAPTER VII 
FLOATING CRUSTACEA OF THE OPEN SEA 

IT is only rarely that the floating organisms of the 
surface of the sea are so large or so abundant 
as to catch the attention of the casual observer. 
Except for an occasional shoal of porpoises or of 
flying-fish, the waste of waters seen from the deck 
of a ship in mid-ocean usually seems to be barren of 
life. Nevertheless, there is probably no region of 
the ocean where the tow-net will not reveal the 
existence of a more or less varied fauna and flora. 
Sometimes, indeed, these organisms, though minute, 
are so numerous as to discolour the water over large 
areas ; whalers in the Arctic seas know by the 
appearance of " whale- food " where whales are likely 
to be found, and herring or mackerel fishermen 
recognize the changes in colour of the water among 
the " signs " which guide them when and where to 
shoot their nets. 

The organisms which make up this " pelagic " 
fauna and flora may be grouped into two classes, 
which may be termed the "swimmers," or Necton, 

138 



PELAGIC FLOATING CRUSTACEA 139 

and the " drifters," or Plankton. The former include 
the larger and more active animals, such as fish, 
whales, and the like, whose movements are more or 
less independent of the movements of the water; 
the latter comprise the plant-life and the floating or 
feebly swimming animals that drift at the mercy of 
waves and currents. A great deal of attention has 
ben given in recent years to the study of the 
plankton, and it has come to be recognized as filling 
a very important place in the balance of life in the 
sea. In the sea, as on land, all the animals are 
ultimately dependent on plants for their food. The 
larger and more conspicuous sea-weeds which grow 
on the sea-bottom, however, can only flourish in 
comparatively shallow water, and the region which 
they occupy forms only a narrow fringe round the 
land-masses of the globe. It is only necessary to 
look at a map of the world, showing the depth of 
the sea, to realize what an insignificant part of the 
area of the oceans contributes in this way to the 
food-supply of marine animals. The microscopic 
plant-life of the plankton, however, makes up for the 
individual minuteness of its constituents by their 
incalculable numbers. The lowly organisms known 
as " diatoms," familiar to the microscopist from the 
beauty of their flinty skeletons, are among the most 
numerous and important of these, and they are 
associated with a great variety of other single-celled 
algae and allied organisms, some of them so minute 



i 4 o THE LIFE OF CRUSTACEA 

that they pass through the finest silk plankton-nets, 
and have to be sought for by special methods of 
collection recently devised for the purpose. All 
these organisms possess the green colouring matter 
(chlorophyll) that enables them to live, as the higher 
plants do, on the carbon dioxide and other sub- 
stances dissolved in the water. The smaller animals 
of the plankton feed on these vegetable organisms, 
and in their turn serve as food for larger animals. 
The Herring, the Mackerel, the gigantic Basking 
Shark, and the still more gigantic Greenland Whale, 
all feed directly on the animal plankton, and we 
have already seen that the animals of the deep sea 
depend entirely on the same source of food-supply. 
Further, very many of the bottom-living animals of 
shallow water swim at the surface in the early stages 
of their life, and feed on the other plankton animals 
and plants. Indeed, it is no exaggeration to say 
that " all fish is diatom " in the same physiological 
sense as " all flesh is grass," and the study of the 
plankton is thus of practical importance as well as 
of scientific interest. 

Of all the minute animals that form the inter- 
mediate links in the chain between diatom and fish 
or whale, the Crustacea are the most important and 
the most numerous both in species and in individuals. 
The Copepoda are more richly represented than any 
of the other groups, and it would be difficult to find 
a sample of marine plankton from which they were 



PELAGIC FLOATING CRUSTACEA 141 

altogether absent. Associated with them we find 
one or two species of Cladocera, a larger number of 
Ostracoda (chiefly of the family Halocypridse), a few 
Mysidacea, the Amphipoda of the suborder Hyperi- 
idea, the Euphausiacea, and some of the shrimp- 
like Decapods ; while the larval stages of these and 
other groups also form an important part of the 
plankton. 

It is necessary to make a distinction between the 
" neritic " plankton of shallow water near the coast 
and the " oceanic " plankton of the open sea. In 
the inshore waters the plankton consists not only of 
organisms that pass the whole of their life at or near 
the surface, but also, and very largely, of the free- 
swimming larvae of bottom-living species, and of 
others that make occasional and temporary excur- 
sions to the surface. For example, if the tow-net 
be used a short distance from land say in some 
sheltered bay on our own coasts the catch will 
often be found to consist largely of larval Crustacea. 
The zoea and megalopa stages of Crabs, the zoea 
and schizopod stages of Prawns and Shrimps, are 
often conspicuous by their numbers, or we may find 
swarms of the nauplius and cypris larvae of Barnacles. 
Sometimes, and especially at night, numbers of 
Cumacea may be found in the tow-net ; and it is 
noteworthy that these are usually males, which leave 
the females burrowing in the mud at the bottom, 
and swarm to the surface for a brief period of 



142 THE LIFE OF CRUSTACEA 

activity. Besides all these more or less temporary 
visitors, however, there are numerous species, even 
in the inshore waters, which are adapted to a 
floating life, and pass their whole existence as 
members of the plankton. Copepoda of many kinds, 
some Mysidae, Amphipods like Hyperia which is 
commonly found sheltering under large jellyfish 
some species of actively swimming Isopods, and 
many other forms, are only to be captured by the 
tow-net ; and now and then, in certain localities, 
winds and currents may drive into coastal waters 
shoals of species whose proper home is the open 
ocean. 

In a similar way the strictly neritic forms may 
sometimes be carried far out to sea, so that it is 
nowhere possible to draw a hard-and-fast line be- 
tween the regions occupied by the neritic and the 
oceanic plankton. With increasing distance from 
land, however, the larval stages of bottom-living 
species become fewer, and finally disappear alto- 
gether, and there is left an assemblage of animals 
whose whole existence is passed floating at the 
surface or at the intermediate depths. How far 
down from the surface this floating fauna actually 
descends is a question which has been much debated. 
It appears now to be certain that there is no stratum 
of water between the surface and the bottom of the 
ocean which is devoid of life, although the upper 
layers (not at, but some distance below, the surface) 



PELAGIC FLOATING CRUSTACEA 143 

are probably much more densely populated than 
those of the abyss. Many of the species appear to 
undertake more or less extensive migrations in a 
vertical direction, coming nearer the surface at 
certain stages of their life-history, and sinking into 
deeper water at others. Further, some species at 
least seem to rise to the surface at night, and to 
sink again during the day. Apart from these vertical 
movements, which are as yet only imperfectly under- 
stood, it is desirable to distinguish between the 
" epiplankton," comprising the organisms which 
inhabit the superficial strata of the ocean down to 
about 100 fathoms, and the " mesoplankton," found 
at greater depths. The plant-life which is dependent 
on sunlight belongs to the epiplankton, while the 
animals of the mesoplankton are dependent, like 
the bottom animals of the deep sea, on the supply 
of dead food material falling from above. A third 
division, the " hypoplankton," has been established 
for those animals which live immediately above the 
bottom, but its distinctness from the mesoplankton 
has not yet been satisfactorily established. Indeed, 
many of the swimming forms which have already 
been mentioned in dealing with the Crustacea of the 
deep sea are probably rather to be considered as 
belonging to the deep mesoplankton at least, where 
their size and swimming powers do not entitle them 
to be ranked with the " necton." 

Many of the modifications in structure character- 



I 4 4 THE LIFE OF CRUSTACEA 

istic of pelagic animals may be traced to the necessity 
for keeping continuously afloat with a minimum of 
exertion. The Crustacea of the plankton never 
carry the heavy armour found in bottom -living 
species. Thus, the thick-shelled Ostracoda of the 
bottom are represented in the plankton chiefly by 
the family Halocypridae (Fig. 48), in which the shell 
is thin, uncalcified, and almost membranous. Many 
species, particularly of the Copepoda, are seen, 




FIG. ^8Conchcecia curta, AN OSTRACOD OF THE PLANKTON, x 40. 
(Partly after G. W. Muller.) 



under the microscope, to have large globules of oil 
distributed through the tissues of the body, and 
these no doubt serve as floats, increasing the 
buoyancy of the animal. The same purpose is 
probably served, in many cases, by having large 
spaces, filled with fluid, within the body. This is 
characteristic of pelagic animals, and is well seen 
in many of the Crustacea in which the viscera and 
muscles occupy a relatively small part of the interior 
of the animals, the intervening spaces being filled 
with colourless transparent fluid. Many of the 



PELAGIC FLOATING CRUSTACEA 145 

Hyperid Amphipoda show this peculiarity for 
example, the relatively gigantic Cystisoma, which is 
mesoplanktonic in deep water; and it reaches its 
extreme in Mimonectes (Fig. 49), in which the anterior 
part of the body is, as it were, blown out into a 




FIG. 49 Mimonectes loveni. A FEMALE SPECIMEN SEEN FROM THE 
SIDE AND FROM BELOW, SHOWING THE DISTENDED-BALLOON- 
LIKE FORM OF THE ANTERIOR PART OF THE BODY. X 3. 
(After Bovallius.) 

balloon, giving the animal the aspect of- a small 
jellyfish rather than an Amphipod. 

If, as seems probable, the body-fluid of these 
animals is of a lower specific gravity than the sea- 
water, it will act like the oil-globules of the Co- 
pepoda in keeping the animals afloat. Even if the 
specific gravity be the same, however, the distension 
10 



146 THE LIFE OF CRUSTACEA 

of the body with fluid acts in another way, by 
increasing the surface exposed to friction with the 
surrounding water, and so retarding sinking. The 




FIG. 50 THE ZOEA LARVA OF A SPECIES OF Sergestes, TAKEN BY 
THE " CHALLENGER " EXPEDITION, x 25. (After Spence Bate.) 

principle involved is illustrated by the fact that a 
soap-bubble sinks much more slowly through the 
air than the drop of water into which it collapses. 



PELAGIC FLOATING CRUSTACEA 147 

The same result is produced if the surface is increased 
by outstanding spines or hairs, just as, for instance, 
a downy feather sinks slowly through the air, but 




FIG. 51 THE NAUPLIUS LARVA OF A SPECIES OF BARNACLE OF 
THE FAMILY LEPADID^E, SHOWING GREATLY-DEVELOPED SPINES. 
FROM A SPECIMEN TAKEN IN THE ATLANTIC OCEAN, NEAR 
MADEIRA, x n. (After Chun.) 



drops rapidly if it is rolled into a ball between the 
fingers. This is, no doubt, one function of the 
spines with which plankton Crustacea, and particu- 
larly larvae, are frequently provided, though they 



148 THE LIFE OF CRUSTACEA 

may also serve in some cases as a protection 
against enemies. The spines have been already 
alluded to in describing the various larvae, but it may 
be noted here that they are most strongly developed 
in larvae which live in the open ocean ; for example, 
the most elaborately armed of all Decapod larvae are 
the zoea stages of Sergestes (Fig. 50), which, like the 




FIG. 52 Calocalanus pavo, ONE OF THE FREE-SWIMMING COPEPODA 
OF THE PLANKTON. ENLARGED. (From Lankester's "Treatise on 
Zoology," after Giesbrecht.) 

adults, belong to the oceanic plankton. The nau- 
plius larvae of Cirripedes are all more or less spiny, 
and the spines reach an exaggerated development in 
the larvae of the genus Lepas (Fig. 51), of which the 
adults are attached to floating drift-wood or the like, 
and belong to the oceanic fauna, although hardly to 
be classed with the plankton. 



PELAGIC FLOATING CRUSTACEA 149 

The large feathered bristles that decorate the 
limbs or tail of many plankton Copepoda have no 
doubt the same function in assisting flotation. In 
the genus Calocalanus (Fig. 52), for example, the 
tail setae are large and brilliantly coloured feathery 
plumes, and in one species, C. plumulosus, one of 
these setae is of relatively enormous size, five or six 
times as long as the body of the animal itself. 

Among the most singular of plankton Crustacea 
are the Phyllosoma larvae (see Fig. 28, p. 72) of the 
Spiny Lobsters and their allies (Scyllaridea), which 
have been already described. These larvae are 
sometimes found far out at sea, and it seems likely 
that their larval life is unusually prolonged, and that 
they may be drifted to great distances by ocean 
currents. At all events, they are well adapted for 
pelagic life, since the broad flat body, hardly thicker 
than a sheet of paper, can be sustained in the water 
like a " hydroplane " by comparatively slight efforts 
of the swimming legs. 

The watery character of the body, together with 
the thinness of the exoskeleton, helps to explain the 
glassy transparency which is a feature of most 
plankton Crustacea. This transparency has been 
regarded as a protective adaptation rendering the 
animals inconspicuous in the water, and it has 
indeed that effect to human eyes, but it is very 
doubtful whether the animals derive much benefit 
from this. Many of the animals such as Herring 



150 THE LIFE OF CRUSTACEA 

and other pelagic fishes that prey upon plankton 
Crustacea appear to swallow them in bulk, with- 
out much selection ; and the Greenland Whale, as 
it swims open-mouthed through the sea, is not likely 
to be guided by the greater or less visibility of the 
Copepods that it sifts out on its baleen plates. 
Further, this glass-like transparency is by no means 
universal, for many plankton Copepoda are brightly 
coloured. In some, as in the beautiful blue Anomalo- 
cera, common in British waters, the colour is due to 
pigment in the fluids and tissues of the body ; in 
others the feathery hairs on the body and limbs 
show brilliant metallic colours, produced, like the 
colours of a peacock's feather, not by pigments, 
but by the diffraction of light in the texture of 
the organ. The most beautiful of all Copepoda is 
Sapphirina, in which the surface of the body 
absolutely sparkles with iridescent colours. 

The striking phenomenon known as the " phos- 
phorescence of the sea " is familiar to every ocean 
voyager, and is seen from time to time on our own 
coast. On a dark night the crest of every wave 
often seems to break in a pale glow, the wake of the 
vessel is a trail of light, and an oar dipped in the 
water seems on fire. This luminosity is due to 
the animals of the plankton, largely to the lowly 
Protozoa and the jellyfishes, but in part also to 
certain Crustacea. A number of pelagic Copepoda 
have been shown by Giesbrecht to secrete, from 



PELAGIC FLOATING CRUSTACEA 151 

special glands on the surface of the body, a sub- 
stance which becomes luminous on coming in contact 
with the water. Even specimens which had been 
dried were found to give out light on being wetted. 
Some pelagic Ostracods of the family Halocypridae 
have been observed to emit clouds of a luminous 
secretion from a gland in the neighbourhood of the 
mouth. A similar habit has been seen, as already 
mentioned, in certain deep-sea Prawns and Mysidacea, 
which may perhaps belong to the deeper part of the 
mesoplankton rather than to the bottom fauna. The 
complex light-producing organs of the Euphausiacea 
have already been described in dealing with deep-sea 
Crustacea. A great many species of this group, 
however, are members of the epiplankton, and in 
these the phosphorescent apparatus is quite as fully 
developed as in species coming from greater depths. 
Meganyctiphanes norvegica (Fig. 24, p. 56), which is 
one of the largest of the Euphausiacea, is common 
at no great depths in many places in British seas. 
If a jar of sea-water in which specimens of this 
species are swimming be brought into a dark room, 
a tap on the glass will cause the photophores to flash 
out like a row of tiny lamps along the side of the 
body. After shining for a few seconds the light dies 
out, to appear again if the tapping be repeated. 

There are certain peculiarities in the structure of 
the eyes in some plankton Crustacea which suggest 
that the sense of sight is of special importance to 



152 THE LIFE OF CRUSTACEA 

their possessors, although we can hardly do more than 
guess at their special significance. Most Copepoda 
have only a single eye in the middle of the head, 
corresponding to the single eye of the nauplius larva, 
and of far simpler structure than the paired com- 
pound eyes of most other Crustacea. In many 
plankton species, however, this simple eye becomes 
much enlarged and complicated in various ways. 
The three parts of which it is normally made up 
may become separated from each other, and are 
sometimes increased in number to five, while lenses 
serving to concentrate the light are often developed 
by thickening of the overlying cuticle. The most 
elaborately constructed eyes are found in the family 
Corycasidse. In Copilia (Fig. 53) a pair of eyes of 
relatively enormous size are present. Each has in 
front a large biconvex lens set at the end of a conical 
tube which extends backwards to a smaller lens (like 
a telescope with object-glass and eyepiece), behind 
which, again, are the sensory cells, corresponding to 
the retina, enclosed in a tube of dark pigment, the 
whole apparatus being more than half the length 
of the body. These eyes, although paired, do not 
correspond to the paired compound eyes of other 
Crustacea, but have arisen by the separation and 
enlargement of two of the three divisions of the 
typical median Copepod eye. 

A peculiarity of the paired compound eyes found 
in plankton Crustacea of several different orders 



PELAGIC FLOATING CRUSTACEA 153 

consists in the division of each eye into two parts, 
which differ in structure. In many Euphausiacea 
and Mysidacea, especially in those haunting the 




FIG. 53 Copilia quadrata (FEMALE), A COPEPOD OF THE FAMILY 

CORYC^EID^E. SHOWING THE PAIR OF LARGE " TELESCOPIC " EYES. 

x 20. (After Giesbrecht.) 

deeper strata (mesoplankton), this division of the 
eyes is well marked, a frontal or dorsal part having 
the separate elements of the eye (ommatidia) greatly 



154 



THE LIFE OF CRUSTACEA 



lengthened and with reduced pigment, while the 
lateral part is of more normal structure. It seems 
probable, from the researches of Professor Chun, 
that the fronto-dorsal division is adapted for the 
perception of very faint light, while the lateral 
division will give a more accurate image of brightly 
illuminated objects. 




FIG. 54 Phronima colletti, MALE. FROM A SPECIMEN TAKEN IN DEEP 
WATER NEAR THE CANARY ISLANDS, x 12. (After Chun.) 

In the pelagic Amphipoda, forming the suborder 
Hyperiidea, the eyes are of very large size, generally 
occupying almost the whole surface of the head, and 
giving the animals a very characteristic appear- 
ance, in contrast to the small-eyed, bottom-living 
Gammaridea. In the family Phronimidae (Fig. 54) 
the eyes are each divided into two parts, differing in 
structure in the way just described. 



PLATE 




Latreillia elegans, ONE OF THE DROMIACEA WHICH RESEMBLES A SPIDER-CRAB. 

FROM THE MEDITERRANEAN. (NATURAL SIZE) 




THE GULF-WEED CRAB, J'/ailCS IllinutllS. (SLIGHTLY ENLARGE!)) 



PELAGIC FLOATING CRUSTACEA 155 

There are a few Crustacea living habitually on the 
high seas which cannot be reckoned as belonging 
either to the true plankton or to the necton, since 
they depend on outside help for keeping themselves 
afloat. Among these are the Barnacles which cluster 
on logs of drift-wood, and are among the most 
important causes of the " fouling " of ships' hulls on 
long voyages. The stalked Barnacles of the genus 
Lepas are especially common in such situations, and 
the characters of their larvae have been already 
alluded to. Certain species of sessile Barnacles are 
constantly found attached to large marine animals. 
For example, Chelonobia adheres to the shell ot 
Turtles, while Coronula and some allied genera are 
found on Whales. 

The little " Gulf-weed Crab " (Planes minutus 
Plate XIX.) is found clinging to floating drift-weed 
nearly everywhere throughout the temperate and 
tropical seas of the globe, and is especially common 
in the area known as the Sargasso Sea, in mid- 
Atlantic. It is occasionally drifted to the south 
coasts of the British Islands. In Sloane's " Natural 
History of Jamaica," published in 1707-1725, it is 
stated of the Gulf- weed Crab that " Columbus, find- 
ing this alive on the Sargasso floating in the sea, 
conceived himself not far from some land, on the 
first voyage he made on the discovery of the West 
Indies." 

A few other Crustacea also form part of the 



156 THE LIFE OF CRUSTACEA 

peculiar fauna which is associated with the Sargasso 
weed, notably a swimming Crab, Neptunus sayi, and 
two or three species of Prawns. All of these are 
coloured olive-green, like the weed among which 
they live. 



CHAPTER VIII 
CRUSTACEA OF FRESH WATERS 

THE Crustacean fauna of fresh water is much 
less rich and varied than that of the sea. 
Although the number of individuals in a pond or 
lake may be enormous, they will be found to belong 
to a comparatively small number of species. All the 
subclasses of Crustacea with the exception of the 
Cirripedia have representatives in fresh water, but 
in most of them only a very few of the families and 
genera comprise truly fresh-water species. In spite 
of the comparative poverty of the fauna, however, it 
is of very great interest, more especially with regard 
to the problems of geographical distribution ; and 
the ease with which specimens may be collected 
everywhere, and kept in small aquaria, renders it 
a particularly attractive subject of study for the 
amateur naturalist. 

The general uniformity of the fresh-water fauna 
throughout the world has often been remarked. 
Darwin says : " When first collecting in the fresh 
waters of Brazil, I well remember feeling much 

157 



158 THE LIFE OF CRUSTACEA 

surprise at the similarity of the fresh-water insects, 
shells, etc., and at the dissimilarity of the surround- 
ing terrestrial beings, compared with those of 
Britain." This uniformity is well illustrated by 
many of the smaller Crustacea. In a gathering of 
Cladocera, Copepoda, and Ostracoda, from Central 
Africa or from Australia, we find that most of the 
genera, and even some of the species, are identical 
with those found in similar situations in this country. 
It is by no means the case that all the species and 
genera are thus universally distributed, for there are 
many, especially among the larger forms, which 
have a very restricted range; but this does not 
render less striking the general uniformity of the 
fauna over very wide areas. 

When we consider the physical environment of 
fresh-water animals, it seems at first sight as if this 
wide distribution were the reverse of what might 
have been expected, for the area occupied by them 
is far more discontinuous than in the case of terres- 
trial or marine animals. The inhabitants of a pond 
or lake are to a great extent isolated ; and although 
they may spread to other ponds and lakes by way of 
communicating streams or rivers, where these are 
not too swiftly flowing and are not interrupted by 
falls, yet direct passage from one river system to 
another is rarely possible. Further, since practically 
the whole of the fresh water on the surface of the 
globe is constantly flowing, more or less rapidly, 



CRUSTACEA OF FRESH WATERS 159 

towards the sea, the smaller feebly swimming forms 
tend to be swept down with the current, and ulti- 
mately carried to perish in the sea. It follows that 
only those forms which possess special adaptations 
for dispersal are able to flourish in fresh water. In 
many cases, as will be described below, the eggs of 
the smaller Crustacea can survive being dried up, 
and in this state they may be blown about by wind 
or carried to great distances in mud, adhering to the 
feet of migratory wading birds. Darwin says : " The 
wide-ranging power of fresh-water productions can, 
I think, in most cases be explained by their having 
become fitted, in a manner highly useful to them, 
for short and frequent migrations from pond to 
pond, or from stream to stream, within their own 
countries ; and liability to wide dispersal would 
follow from this capacity as an almost necessary 
consequence " (" Origin of Species," sixth edition, 
chapter xiii.). In accordance with this, we find that 
it is just those groups of Crustacea which show these 
adaptations for dispersal that are most universally 
distributed in fresh water. On the other hand, the 
larger Crustacea, like the Crayfishes and River 
Crabs, which cannot so easily be transported from 
one locality to another, have as a rule a more 
restricted range. These larger forms, from their 
size and powers of swimming or creeping, can make 
their way upstream and spread throughout a river 
system, and in some cases they can leave the water 



160 THE LIFE OF CRUSTACEA 

and journey for short distances overland. On the 
other hand, since free-swimming larvae would be 
liable to be swept out to sea, most of them have 
a direct development, the young only leaving the 
protection of the mother when they have attained 
the form and habits of the adult. When all these 
factors have been taken into account, however, there 
still remain many cases where the distribution of 
individual species or of groups is hard to explain, 
and shows indications of dating from a time when 
the outlines of continents and the connections of 
river systems were different from what they are now. 

Before proceeding to mention some of the more 
characteristic forms of fresh-water Crustacea, it 
should be mentioned that in large lakes, as in the 
sea, we can distinguish a littoral fauna in the shallow 
waters close to the shore, a plankton fauna of the 
surface waters, and a deep-water fauna. The littoral 
fauna does not differ in general characters from that 
found in smaller ponds and gently-flowing rivers; 
the plankton comprises many peculiar species show- 
ing adaptations for flotation, as in the case of the 
marine plankton ; and the deep-water fauna is very 
poor in species and in individuals, and shows some 
relations with the subterranean fauna to be men- 
tioned later. 

Of all the subclasses of Crustacea, the Branchio- 
poda are the most characteristically fresh-water 
animals, only a few Cladocera being found in the 



CRUSTACEA OF FRESH WATERS 161 

sea, and some Anostraca in salt lakes and brine 
pools. 

The larger Branchiopoda (Anostraca, Notostraca, 
and Conchostraca) are generally found in small, 
shallow ponds which are liable to be dried up 
in summer. The " Fairy Shrimp " (Chirocephalus 
diaphanus; see Fig. 10, p. 35) has been found in 
swarms in the water standing in deep cart-ruts in 
a country lane in England, and Apus sometimes 
appears suddenly in rain-water puddles of a few 
square yards in area, which dry up after a few weeks 
of hot weather. The eggs of these animals, when 
dried in the mud, may remain dormant for long 
periods, and many species have been hatched out 
from samples of dried mud brought by travellers 
from distant countries. In such a sample from the 
Pool of Gihon at Jerusalem, it is recorded that the 
eggs of Estheria (see Fig. n, p. 36) were found to 
be capable of hatching after being kept dry for nine 
years. In some species it is said that the eggs will 
not develop unless they have been first dried, but 
this is not the case with Chirocephalus. In favour- 
able conditions development takes place very rapidly. 
Messrs. Spencer and Hall, in describing the Branchi- 
opoda of Central Australia, say : " Certainly not more 
than two weeks after a fall of rain, and probably 
only a few days, numberless specimens of Apus, 
measuring in all about 2| to 3 inches in length, were 
swimming about ; and, as not a single one was to be 
ii 



162 THE LIFE OF CRUSTACEA 

found in the water-pools prior to the rain, these 
must have been developed from the egg." 

From what has been said, it is apparent that the 
larger Branchiopoda are particularly well fitted to 
be distributed by the agency of birds, and this is no 
doubt the explanation of the way in which many of 
the species suddenly appear in localities where they 
were previously unknown, and, after swarming for 
a longer or shorter time, sometimes for several suc- 
cessive seasons, as suddenly vanish. A striking 
example of this is afforded by Apus cancriformis 
(see Plate II.), which formerly occurred in several 
localities in the South of England, and appears more 
or less irregularly in many parts of the Continent of 
Europe. No British specimens had been recorded 
for over forty years, and the species was believed to 
be extinct in this country, when it was found in 1907 
by Mr. F. Balfour Browne in a brackish marsh near 
Southwick, in Kirkcudbrightshire. It can hardly be 
supposed that so large an animal as Apus, and one 
so easily recognized, would have escaped notice alto- 
gether had it occurred regularly in any part of the 
British Islands. It is much more probable that the 
Scottish specimens found in 1907 had developed 
from eggs accidentally transported by some bird 
from the Continent. In 1908 a careful search 
in the same locality failed to reveal a solitary 
specimen. 

The Anostraca and Notostraca usually swim with 



CRUSTACEA OF FRESH WATERS 163 

the back downwards. Particles of mud and of animal 
and vegetable matter are drawn by the currents pro- 
duced in swimming, into the ventral groove between 
the pairs of feet, and are passed forwards to the 
mouth to serve as food. Some species of Conchos- 
traca are said to swim in the same inverted position ; 
but Messrs. Spencer and Hall, in the memoir already 
quoted, state that the Australian Conchostraca swim 
back uppermost. They attribute the difference in 
habit between the Conchostraca and Notostraca 
to the fact that in the former group the valves of 
the shell can be rapidly closed to protect the soft 
and vulnerable appendages, while no such protection 
is possible in the Notostraca. They found on one 
occasion a specimen of Apus (Notostraca) attacked 
by three Water-beetles, which were tearing its soft 
appendages, and they suppose that Apus generally 
escapes such attacks by swimming upside down. 

The breeding habits of the Branchiopoda are also 
of interest, from the prevalence in many species of 
reproduction by unfertilized eggs, or "partheno- 
genesis." This may go on for many generations, 
and in Apus, for instance, it is possible to examine 
thousands of specimens before rinding a single male, 
although, for some unexplained reason, males are 
sometimes comparatively common. It is probable 
that males must appear sooner or later, otherwise 
the series of parthenogenetic generations will come 
to an end; but it is not certain that this is the 



164 



THE LIFE OF CRUSTACEA 



case, and there are some species of Conchostraca 
of which the males have never been seen. 

The genus Artemia (Fig. 55), among the Anostraca, 
is peculiar in its habitat ; for, while most of the 



B. 




FIG. 55 THE BRINE SHRIMP (Artemia salina). (After Sars.) 

A, Female, under-side, x 6 ; B, head of male, upper side, further 
enlarged, showing the large clasping antennae. The larval 
stages of this species are shown in Fig. 33, p. 81 

Branchiopoda inhabit fresh or brackish water, it 
flourishes in concentrated brine. In the South of 
Europe it is found, as it was formerly in England, 
in the shallow ponds in which sea-water is exposed 



CRUSTACEA OF FRESH WATERS 165 

to evaporation for the manufacture of salt, and in 
these it occurs in such numbers as to give the water 
a reddish colour. It is also found in salt lakes, like 
the Great Salt Lake of Utah, in the United States, 
and in many other parts of the world. The specimens 
from different localities often differ considerably, 
especially in the form of the tail-lobes ; but it has 
been shown that these differences are more or less 
directly correlated with the degree of salinity of the 
water in which the animals live, and it is probable 
that the forms which have been described are all 
variations of a single cosmopolitan species ranging 
from Greenland to Australia, and from the West 
Indies to Central Asia. A rtemia is the only one of 
the Anostraca that is known to be parthenogenetic, 
some colonies consisting entirely of females, while 
in others males are abundant. The reddish colour 
above alluded to is found also in Branchipus, Apus, 
and other Branchiopoda, and is due, as Sir Ray 
Lankester first showed, to the presence in the body- 
fluids ot haemoglobin, the red colouring matter of 
the blood of Vertebrates, which is important in the 
process of respiration. 

The smaller Branchiopoda known as " Water-fleas," 
forming the order Cladocera, are abundant every- 
where in fresh water. Daphnia pulex and other 
speces of the genus, and the little Lynceidae, of 
which Chydorus sphcericus (Fig. 56) is the commonest 
species, are to be found in ponds and ditches, and 



i66 



THE LIFE OF CRUSTACEA 



the shell. 




often swarm in farmyard ponds where the water is 
foul with decaying matter. In most gatherings from 
such localities only female specimens will be found, 
and nearly all of these will be seen to carry a cluster 
of eggs or of developing embryos in the " brood- 
chamber " between the back part of the body and 
In Daphnia pulex (see Fig. 12, p. 37) a 
single brood may consist of 
thirty young, and occasionally 
of more than twice that number. 
As the broods may succeed each 
other at intervals of two or 
three days, it will be seen that 
the multiplication of the species 
in favourable circumstances may 
be exceedingly rapid. It has 
been calculated that in sixty 
days the progeny of a single 
female might amount to about 13,000,000,000. In 
addition to these parthenogenetic eggs, which hatch 
at once while still within the brood-chamber, the 
Cladocera produce, at certain seasons, another kind of 
egg which requires to be fertilized by the male before 
it will develop. These eggs are dark in colour and 
are enclosed in a thick shell, and they do not hatch 
at once, but are cast off when the shell of the female 
is moulted. Very commonly these " resting eggs," 
as they are called, are produced in the autumn and 
lie dormant until the following spring, and they can 



FIG. 56 Chydorus 
spharicus, A COMMON 
SPECIES OF WATER- 
FLEA, x 50. (After 
Lilljeborg.) 



CRUSTACEA OF FRESH WATERS 167 




survive drying or freezing without injury, while the 
thin-shelled parthenogenetic eggs within the brood- 
chamber of the mother are easily killed. In addition 
to having thick shells, the resting eggs are further 
protected in most, but not in all, cases by the 
moulted carapace of the parent, which is specially 
thickened for the purpose. 
This modification of the cara- 
pace is most highly developed 
in the family Daphniidae 
(Fig. 57), where a saddle- 
shaped area on the dorsal 
side, known as the " ephip- 
pium," becomes thickened, 
and on moulting separates 
from the rest of the carapace 
to form a compact case en- 
closing the two resting eggs. 
The outer wall of the ephip- 
pium is divided up into small 
hexagonal cells, which become filled with air, causing 
the ephippium to float at the surface of the water. 
In this position the ephippia readily become en- 
tangled in the feathers of birds, and in some cases 
the shell is provided with spines or hooks, which 
facilitate transport to other localities by such means. 
The appearance of males and the production of 
ephippial eggs in other words, the "sexual period" 
is generally more or less restricted to one season 



FIG. 57 A WATER-FLEA, 
(Daphnia pulex), FEMALE, 

WITH EPHIPPIUM CON- 
TAINING Two " RESTING 
EGGS." x 20. (Partly 
after Lilljeborg.) 
The Antenna is cut short. 
Compare Fig. 12, p. 37. 



168 THE LIFE OF CRUSTACEA 

of the year. In most species, particularly in those 
which live in lakes, the sexual period occurs in the 
late autumn, and the ephippial eggs lie dormant 
during the winter, and hatch in the spring. In 
species living in small ponds exposed to the risk of 
overheating or of drying up during summer, there is 
often a distinct sexual period in the spring, when 
ephippial eggs are produced to tide over the un- 
favourable conditions of the warmer months of the 
year. Although no species is known to be exclusively 
parthenogenetic, yet it appears that purely partheno- 
genetic colonies of certain species may be found in 
favourable localities, where they may reproduce from 
year to year without males ever being found. 

Certain species of Cladocera belong to the plankton 
of lakes and large ponds, and show modifications 
which adapt them for a floating life. Some of these 
belong to the genus Daphnia, and differ from the 
species found in other situations by their glassy 
transparency. As in the case of many marine 
plankton Crustacea, this transparency is probably 
due to the thinness of the shell and to the general 
watery condition of the body, giving the necessary 
buoyancy to enable the animal to remain constantly 
afloat. The same effect is no doubt produced by the 
long terminal spine of the carapace and by the great 
helmet-shaped crest into which the upper part ot 
the head is often produced. A form very character- 
istic of the plankton of large lakes is Bythotrephes' 



CRUSTACEA OF FRESH WATERS 169 

(Fig. 58), which is found in the lakes of Scotland, 
Ireland, Wales, and the Lake District of England. 
In Bythotrephes the carapace does not enclose the 
body, but is reduced to a small brood-sac ; the 
addomen, however, is drawn out into a long spine, 
which may be two or three times as long as the 
body. A further point of interest is the division of 
the eye into a dorsal and a ventral portion, differing 




^& 

FIG. 58 Bythotrephes longimanus, FEMALE, WITH EMBRYOS IN THE 
BROOD-SAC, x 12. (After Lilljeborg.) 



in structure in much the same way as do the two 
divisions of the eyes in certain marine plankton 
Crustacea (see p. 152). Another very remarkable 
lacustrine form is Leptodora, the largest of all the 
Cladocera, being sometimes more than half an inch 
in length. In this case also the carapace is very 
small, and does not enclose the body. The swimming 
antennae are very large, and the abdomen is long and 
divided into several segments. 

Leptodora is further remarkable on account of its 
mode of development. The parthenogenetic eggs, 



170 THE LIFE OF CRUSTACEA 

as in other Cladocera, develop directly, but the 
resting eggs give rise to larvae of the nauplius type. 

Holopedium, which is found in similar situations, 
surrounds itself with a mass of a jelly-like substance 
which it secretes. A similar envelope of jelly is 
found in some marine plankton animals, though not, 
so far as is known, in any Crustacea, and it no 
doubt serves to give buoyancy to the animal. 

The Copepoda of fresh water are as abundant and 
universally distributed as the Cladocera. Species 
of the genus Cyclops (see Fig. 14, p. 39), easily 
recognized by the pear-shaped body and the two 
egg-packets carried by the female, are to be found in 
almost every pond and ditch. The genus Cantho- 
camptus comprises species of smaller size, with 
slender, flexible body, and carrying only a single 
egg-packet. The plankton of lakes and ponds 
includes species of Diaptomus (Fig. 59), which have 
a narrow body and very long antennules. The latter 
are held out stiffly while the animal swims by rapid 
movements of the antennae and mouth parts, making 
occasional sudden leaps by means of its oar-like feet. 
In this genus also the egg-packet is single. The 
development can easily be studied by keeping egg- 
carrying females of Cyclops in a jar of water, when 
the nauplius larvae will soon hatch out. 

Although the Copepoda, unlike the Cladocera, are 
not parthenogenetic, it has been found that certain 
species of Diaptomus produce resting eggs capable of 



CRUSTACEA OF FRESH WATERS 171 

surviving freezing or drying. In the early part of 
the breeding season the eggs have thin shells, and 
they hatch after a short time. In the autumn, 
however, thick-shelled eggs are produced, which lie 
dormant in the mud until the following spring. It 
has recently been discovered that species of Cyclops 
and Canthocamptus pass through a resting stage, in 




FIG. 59 Diaptomus casruleus, FEMALE, x 25. (After Schmeil.) 

which the animal surrounds itself with a cocoon-like 
capsule of mud held together by a glutinous secretion 
produced by glands on the surface of the body and 
limbs. The encapsuled animals, in the cases 
observed, lie dormant in the mud during the 
summer, to resume active life in the colder months 
of the year. It is very probable that they can also 
be dried without injury, and that the " cocoons " 



172 THE LIFE OF CRUSTACEA 

serve the same purpose as the resting eggs of other 
species. 

Numerous species of Ostracods, belonging to the 
genus Cypris (see Fig. 13, B, p. 38), and other closely 
related genera, occur in fresh water. Like the 
Cladocera, they reproduce largely by partheno- 
genesis, and the males of many species are rarely 
found, while in some species they have not yet been 
discovered. In Professor Weismann's laboratory 
at Freiburg a colony of Cypris was kept in an 
aquarium for eight years, and during the whole of 
that time no males made their appearance, the 
colony reproducing exclusively by parthenogenesis. 
Probably in all species the eggs survive drying. 

The common " Freshwater Shrimp " (Gammarus 
pulex), which has already been described, may be 
taken as a type of a large number of Amphipoda, for 
the most part closely allied, which are widely dis- 
tributed in most regions of the world, with the 
exception of the tropics. G. pulex itself ranges from 
the British Islands to Mongolia. As the eggs 
are carried, till they hatch, in the brood-pouch of 
the parent, and are not known to survive drying, it 
is difficult to understand in what way Gammarus 
and its allies contrive to spread from one locality 
to another. 

The little fresh-water Isopod Asellus aquations 
(Fig. 60) is common in ponds and canals in this 
country. It may be recognized by its general resem- 



CRUSTACEA OF FRESH WATERS 173 

blance to a Woodlouse, with very long antennae, and 
with a pair of long, slender, forked uropods project- 
ing behind. The species is widely distributed in 
Europe, and other species of the same and closely 
related genera are found in North America. 

In Australia and New Zealand the Isopoda are 
represented in fresh waters by a very peculiar group 




FIG. 60 Asellus aquaticus, FEMALE, x 4. (After Sars.) 

of species, forming the suborder Phreatoicidea, 
which have more the aspect of Amphipods than of 
Isopods, since the body is more or less flattened 
from side to side, instead of from above downwards. 
With regard to the mode of distribution of the 
fresh-water Isopoda, there is the same difficulty as 
in the case of the Amphipoda, for the eggs are 



174 THE LIFE OF CRUSTACEA 

carried in a brood-pouch, and do not seem to be in 
any way protected against drought. It is no doubt 
in consequence of this that the fresh-water species 
and genera of both Amphipoda and Isopoda, though 
widely distributed, do not have the world - wide 
range of many of the more minute Crustacea 
described above. 

The common Crayfish, Astacus (or Potamobius) 
pallipes, is the only truly fresh-water Decapod found 
in England, although a small Prawn, Palcemonetes 
varians, which usually inhabits brackish water, may 
occasionally be found in places where the water is 
practically fresh. The structure of the Crayfish is 
very similar to that of the Lobster, but, as already 
mentioned, it differs in its mode of development, 
having no free-swimming larval stage. From its 
size, and from the fact that the eggs are carried by 
the female, the Crayfish cannot be transported from 
one locality to another by the agencies which dis- 
tribute the smaller fresh-water Crustacea. On the 
other hand, the adult animals can live out of the 
water for days, or even weeks, if they are kept moist, 
and the English species is stated to leave the water 
occasionally, and to make short excursions on land. 
Many species found in foreign countries are still 
more truly amphibious in their habits. It is clear, 
however, that the means of dispersal of the Cray- 
fishes are very limited, and on this account the 
problems connected with their geographical distribu- 



176 THE LIFE OF CRUSTACEA 

tion are of great interest. An admirable discussion 
of the subject will be found in Professor Huxley's 
book on the Crayfish, and the conclusions reached 
by him have hardly been modified by thirty years 
of subsequent research. Only a very brief outline 
can be attempted here. 

Crayfishes are found in the fresh waters of the 
Northern and Southern Hemispheres (Fig. 61), but in 
each case they are practically confined to the tem- 
perate regions, and are absent from a broad inter- 
vening tropical zone. The Northern Crayfishes, 
forming the family Astacidas (or Potamobiidse) are 
distinguished, among other characters, by having a 
pair of appendages on the first abdominal somite, 
at least in the male sex ; the Southern Crayfishes 
have no appendages on that somite, and for this and 
other reasons are regarded as constituting a distinct 
family Parastacidae. There is thus a general corre- 
spondence between the geographical distribution of 
the Crayfishes and the more important structural 
differences expressed in their classification. There 
can be no doubt that the two families have been 
derived from a common stock of marine lobster-like 
animals, and it is reasonable to suppose that two 
branches of this stock became independently adapted 
to a fresh-water habitat in the North and in the 
South, giving rise to the Astacidae and the Par- 
astacidae respectively. 

The distribution of the individual genera is, how- 



PL A TE X.\' 




5'H 




\\ 



CRUSTACEA OF FRESH WATERS 177 

ever, not so easy to understand. The species found 
in Europe all belong to the genus Astacus, which 
also penetrates into Asia as far as Turkestan and the 
basin of the River Obi. 

Throughout the greater part of Asia no Crayfishes 
are found until we come to the Far East, where we 
find an isolated colony in the river-system of the Amur, 
in Korea, and in the north of Japan. These far eastern 
Crayfishes, however, differ so much from the typical 
species of Astacus that they are now placed in a 
subgenus (sometimes regarded as a distinct genus), 
Cambaroides. Curiously enough, the typical genus 
Astacus reappears again on the other side of the 
Pacific, where several species occur in that part of 
North America which lies west of the Rocky Moun- 
tains. East of the Rockies, again, numerous species 
are found belonging to a distinct genus, Cambarus, 
which ranges from Canada to Central America and 
Cuba, and this genus is allied in certain respects to 
the Cambaroides of Eastern Asia. If the systematic 
relations of these genera have been properly inter- 
preted, it is by no means easy to understand in what 
way their present distribution has been brought 
about. 

The Southern Crayfishes have an even more scat- 
tered and discontinuous range. In New Zealand the 
genus Paranephrops occurs, in Australia and Tasmania 
the genera A stacopsis (Plate XX.), Cheraps&ndEngceus 
(Plate XX.). A single species of Cheraps has been re- 
12 



178 THE LIFE OF CRUSTACEA 

corded from New Guinea, but no Crayfishes are found 
in any part of the Malay Archipelago, in Southern 
Asia, or on the continent of Africa, although, 
curiously enough, a single species of a peculiar 
genus (Astacoides) is found in Madagascar. In South 
America species of Parastacus are found in Southern 
Brazil, Argentina, and Chili. It is evident that 
these various genera of Parastacidse, which are now 
so widely isolated from each other, must have reached 
their present habitats when the relative distribution 
of land and sea in the Southern Hemisphere was 
very different from what it is now. What exactly 
the nature of the land connection between the various 
islands and continents was, whether by way of an 
Antarctic continent or otherwise, is a question that 
can only be suggested here. To attempt to answer 
it would involve the consideration of the distribution 
of many other groups of animals besides Crayfishes. 
Before leaving the Crayfishes, it may be mentioned 
that certain species have become adapted to almost 
terrestrial habits. A number of species of Cambarus 
in North America are often found at considerable 
distances from open water, burrowing in damp earth, 
their burrows reaching down to the ground-water. 
In many cases they throw up chimney-like piles of 
mud at the mouths of their burrows, and in places 
their chimneys are so numerous as to " hamper 
farming operations by interfering with the harvesting 
machines, clogging and ruining them." The species 



PLATE XXI 




CRUSTACEA OF FRESH WATERS 179 

of Engceus (Plate XX.), found in Tasmania, are there 
known as " Land Crabs," and burrow in marshy 
places and in the forests up to an elevation of 
4,000 feet. 

The broad equatorial belt which separates the 
regions inhabited by the Northern and the Southern 
Crayfishes is characterized by the presence of several 
other groups of fresh-water Decapoda. The large 
River Prawns, which are found nearly every- 
where within the tropics, belong to the genus 
Palcemon (Plate XXL), which is very closely related 
to the common marine Prawns (Leander) of our own 
coasts. Some of these Prawns grow to a foot or 
more in length of body, and the large claws may 
measure as much again. From the Crayfishes, for 
which they are sometimes mistaken, they may be 
easily distinguished by the fact that the large pincer- 
claws are not the first, but the second pair of legs. 
Another widely-spread group of River Prawns, for 
the most part of small size, is the family Atyidae 
(Plate XXII. ), in which the two pairs of pincer- 
claws are feeble, and have the fingers tipped with 
brushes of long hairs, used in sweeping up minute 
particles of food from the mud. The distribution of 
these Prawns presents many difficult problems, as an 
example of which we may mention the presence of 
identical or closely related species in the fresh waters 
of West Africa and of the West Indies. 

The Brachyura (or Crabs) include many species 



i8o THE LIFE OF CRUSTACEA 

that live in fresh water. Some of these, like the 
species of Sesarma (see Plate XXIII.) and some other 
genera of the family Grapsidae, are common through- 
out the tropics, passing up the rivers from the 
brackish water of estuaries, and being often found 
long distances inland in quite fresh water. The true 
River Crabs, however, belong to the family Potamo- 
nidae, and are very common throughout the warmer 
regions of the globe. One species, Potamon edule 
(Plate XXIII.), formerly called Telphusa fluviatilis, is 
found in the South of Europe (Italy, Greece, etc.). 
Very numerous species, as yet only imperfectly 
known, occur throughout the whole of Africa, in 
Southern Asia, and in the Malay Islands, extending 
to Australia in the south and Japan on the north. 
In the New World the River Crabs are found in 
South America, and extend north to Mexico and the 
West Indian Islands. Many of the River Crabs are 
amphibious in habits, and may be found burrowing 
in marshy ground or in damp forests. The young 
are hatched from the egg with all the appendages 
developed, and they remain clinging to the abdomen 
of the mother until after the first moult, when they 
are perfectly-formed little crabs (see Fig. 31, p. 78). 

The groups which have been mentioned are all 
characteristic inhabitants of the fresh waters over 
considerable areas of the surface of the globe. There 
are, however, in addition to these, certain Crustacea 
which occur in isolated localities, and have no close 



PLATE XXII 




CRUSTACEA OF FRESH WATERS 181 

allies in fresh waters elsewhere. In the streams of 
Southern Brazil and Chili there is found a small 
Crustacean (JEglea Icevis Plate XXIV.), not unlike 
the Galatheas of our own coasts, which is interesting 
as being the only species of the Anomura found in 
fresh water. Still more remarkable are the Syn- 
carida, which are represented by two species of 
" Mountain Shrimps " (see Fig. 84, p. 264) in Tas- 
mania, and by a third species found near Melbourne. 
These forms have no near allies among living 
Crustacea, but appear to be related, as will be shown 
in a later chapter, to certain fossil Crustacea found 
in Palaeozoic rocks. 

Belonging to a different category from any of 
those mentioned are certain Crustacea closely allied 
to, or identical with, species living in the sea, which 
inhabit inland lakes where no direct passage from 
the sea is now possible. Attention was first called 
to these in the case of some of the large lakes of 
Sweden, in which Professor Loven found some Crus- 
tacea Mysis relicta (see Fig. 16, p. 47), Mesidotea 
entomon, Pontoporeia affinis almost or quite identical 
with species inhabiting the Baltic, the Arctic Ocean, 
and the North Atlantic. There is geological evidence 
to show that these lakes were once fjords, or arms 
of the sea, and have become cut off from com- 
munication with the Baltic by gradual elevation of 
the land. The marine animals which they contained 
would thus be imprisoned, and as the water became 



i82 THE LIFE OF CRUSTACEA 

less and less salt, by the inflow of rivers, certain 
species which were able to accommodate themselves 
to the altered conditions would survive. Some of 
the species living in the Swedish lakes have since 
been found to have a wider distribution. Thus, 
Mysis relicta, which should perhaps be reckoned as 
only a variety of the Mysis oculata of Arctic seas, has 
been found in lakes in Russia, North Germany, and 
North America (Lake Superior and others), and has 
lately been discovered in Lough Neagh and some 
other lakes in Ireland. 

The brackish waters of the Caspian Sea contain a 
very remarkable assemblage of animals, including 
many Crustacea, which, although now quite isolated 
from the oceans, are certainly of marine, and in part 
of Arctic, origin. Among these are some species 
closely allied to or identical with those of the Swedish 
lakes already mentioned, together with a great variety 
of species of Mysidacea, Cumacea, and Amphipoda, 
which appear to have been evolved from marine 
forms since the Caspian was cut off from communica- 
tion with the Arctic Ocean. 

To such assemblages of animals derived from 
marine species and isolated in inland lakes the name 
of " relict " faunas has been given. It is necessary to 
use caution, however, in extending this explanation 
of their origin to every case of peculiar lake faunas. 
For example, there are difficulties in the way of 
supposing that Lake Baikal was ever in open and 



PLATE XXfll 




THE RIVER-CRAB OK SOUTHERN EUROPE, Potauion edule (OR Telphusa JJuviatilis) 
(REDUCED) 




Scsarma chiragra^ A FRESHWATER CRAB OF THE FAMILY GRAPSID.U. 

FROM BRAZIL. (SLIGHTLY REDUCED) 



CRUSTACEA OF FRESH WATERS 183 

direct communication with the sea, although it con- 
tains many animals, such as seals, which are certainly 
of marine origin. The chief Crustacea of the lake are 
numerous species of Amphipods belonging to the 
genus Gammarus, and other genera closely related 
thereto, and for these, at all events, there is no need 
to assume a " relict " origin. 

One of the most remarkable lakes in the world 
from a zoological point of view is Lake Tanganyika 
in Africa. When it was found that this lake con- 
tained a fauna very different from that of the other 
great lakes of Africa, it was rashly assumed that it 
must be of relict origin, and some remarkable specula- 
tions were indulged in as to the former connection 
between the lake and the sea. Further research, 
while it has greatly emphasized the peculiar nature 
of the fauna, has entirely disposed of the view that 
it originated in this way. The Crabs and Prawns, 
for example, are not nearly related to marine forms, 
but belong to groups that are characteristic of fresh 
waters in the tropics. While Nyassa and the 
Victoria Nyanza have as yet only yielded a single 
species of Prawn, and that one of enormously wide 
distribution (from the Nile to Queensland), Tangan- 
yika contains no fewer than twelve species, all of 
which are peculiar to the lake, while all except one 
belong to genera unrepresented elsewhere. Similarly, 
the Crabs found in the other great lakes of Africa 
belong to commonplace types of River Crabs of the 



184 THE LIFE OF CRUSTACEA 

genus Potamon ; in Tanganyika, in addition to some 
of these, there are three species of a remarkable 
genus, Platytelphusa, not known from any other 
locality. The Copepoda and Ostracoda of Tangan- 
yika comprise a remarkably large number of species, 
many of them peculiar to the lake. A most unusual 
feature is the entire absence of Cladocera. It is not 
easy to explain the occurrence of this remarkable 
fauna in Tanganyika, but the evidence from other 
groups of animals, such as Mollusca and fishes, tends 
to suggest that the lake must have been, until recently, 
completely isolated from the other lakes and river- 
systems of Africa, that it had no outlet, and that the 
water was consequently more or less brackish. 
Under these conditions the fauna of the lake, 
originally similar to that of the other African lakes, 
has evolved along lines of its own. 

A very interesting division of the fresh-water fauna 
is constituted by those animals which inhabit under- 
ground waters. In the South of England there is 
found not unfrequently in the water of wells a small 
colourless transparent Amphipod known as the 
" Well Shrimp " (Niphargus aquilex Fig. 62), distin- 
guished from the common fresh- water Gammarus by 
the slenderness of its body, by the elongation of the 
last pair of tail appendages (uropods), and by the 
absence of eyes. The proper habitat of Niphargus is 
not actually in the wells, but in the subterranean 
reservoirs and streams by which the wells are fed. 



PLATE XXIV 




lievis. SOUTH AMERICA. (NATURAL SIZE) 



CRUSTACEA OF FRESH WATERS 185 

These subterranean channels intercommunicate over 
wide areas, and are now known in many parts of the 
world to contain a peculiar assemblage of animals 
which become accessible to the naturalist in wells and 
in the streams and lakes of large caves. Further, 
the scanty " abyssal " fauna of deep lakes is partly 
made up of species which enter the lakes by sub- 




FIG. 62 A WELL SHRIMP (Niphargus aquilex). X 7. (After 
Wrzesniowski.) 

terranean channels, and find a suitable habitat in 
the deep water. Species of Niphargus, for example, 
have been dredged in Lough Mask in Ireland and in 
some of the Swiss lakes. 

Several species of blind Crayfishes have been found 
in caves in North America, the best known being one 
(Cambarus pellucidus Plate XXV.) found in the 
Mammoth Cave in Kentucky ; and blind Prawns 



i86 THE LIFE OF CRUSTACEA 

belonging to various genera have been discovered in 
caves in America and Europe. 

A very remarkable feature of the subterranean 
fauna is that a number of the animals appear to be 
more closely allied to marine species than to any 
known from fresh waters above-ground. This is 
especially the case with some of the Isopoda belong- 
ing to typically marine families like the Cirolanidse 
and Anthuridae, and it has been suggested that these 
have been derived from marine species which have 
entered the underground waters directly from the sea 
by way of submarine fissures in the crust of the 
earth. 

The environment in which these subterranean 
animals live resembles that of the deep-sea animals 
in the absence of light, and the consequent absence of 
plant-life. They must ultimately depend for food on 
animal and vegetable debris washed down from the 
surface, but the food-supply must be scanty, for the 
water in which they live is usually very clear and 
free from organic matter. It is not surprising to find 
that nearly all of them are blind, and the few species 
provided with visual organs which have been described, 
from caves, are probably only temporary or accidental 
immigrants. Whether the degeneration of the eyes 
is the direct effect of disuse, or is due to natural 
selection ceasing to keep the eyes up to the standard 
of usefulness, is a question which has been much 
debated, and its answer, were we sure of it, would 



PLATE XXV 




THE BLIND CRAYFISH OF THE MAMMOTH CAVE OF KENTUCKY, 

Ca.tnba.i~us pellucidus. (NATURAL SIZE) 



CRUSTACEA OF FRESH WATERS 187 

settle some of the most fundamental problems of the 
evolution theory. 

At all events, we do not find in any truly subter- 
ranean species large and peculiarly modified eyes 
like those of many deep-sea animals, and this may 
be associated with the complete darkness of their 
habitat, not lighted by phosphorescent organisms as 
the deep sea is. In another respect these animals 
differ from those of the deep sea, for they are all 
colourless or nearly so ; while many of the inhabitants 
of the deep sea, as we have already seen, are brilliantly 
coloured. 




CHAPTER IX 
CRUSTACEA OF THE LAND 

THERE is every reason to believe that the 
Arthropoda, like the other great groups of 
the animal kingdom, had their origin in the sea ; but 
they must have invaded the dry land at a very early 
period, and most of the classes into which the group 
is divided the Arachnids, Myriopods, and Insects 
are now predominantly terrestrial in their habits. 
The Crustacea alone have remained for the most 
part aquatic animals, and only in a comparatively 
few cases have they succeeded in adapting them- 
selves completely to an air-breathing existence. As 
already mentioned, a considerable number, both of 
marine and of fresh-water species, are more or less 
amphibious in their habits. Thus, the common 
Shore Crab of our own coasts and the Grapsoid 
Shore Crabs of warmer seas voluntarily leave the 
water and scramble about among the rocks between, 
and even above, tide - marks. Some Crabs, like 
Ocypode and Gelasimus (see Plate XV.), have gone 
farther towards becoming land-dwellers, since their 
188 



CRUSTACEA OF THE LAND 189 

gill chambers are adapted to serve as lungs for 
breathing air, and some species may even be drowned 
by keeping them in water. The marsh-dwelling 
or fresh-water Crabs of the genus Sesarma (see 
Plate XXIII.) and allied genera are also apparently 
to some extent air-breathers, and one species, Aratus 
pisonii, is stated by Fritz Miiller to climb mangrove 
bushes and to feed on their leaves. Some Crayfishes, 
like the Engceus of Tasmania (see Plate XX.), already 
mentioned, are practically land animals. Finally, 
some Amphipoda, closely allied to the Sand-hoppers 
of British coasts, live in damp places on land, 
although they do not show any conspicuous modi- 
fications of structure to adapt them to this mode of 
life. Of one of these Amphipoda, Talitrus sylvaticu.s, 
Mr. G. Smith writes : " This species of land-hopper 
is widely distributed in the highlands of Tasmania, 
being found under logs and leaves in the forests on 
Mount Wellington, and in very great abundance in 
the beech -forests on the mountains of the west 
coast." 

It will thus be seen that it is impossible to draw 
any sharp distinction between aquatic and terrestrial 
Crustacea, and it is chiefly from motives of con- 
venience that we have left to be dealt with in this 
chapter three groups of land-dwelling Crustacea 
the Land Crabs of the family Gecarcinidse, the 
Land Hermits (Coenobitidse), and the Land Isopods, 
or Woodlice (Oniscoidea). 



igo THE LIFE OF CRUSTACEA 

The Gecarcinidae are abundant in the tropics of 
the Old and New Worlds. Some of the species at 
least, probably all, visit the sea at intervals for the 
purpose of hatching off the eggs carried by the 
females, and the larval stages are passed in the sea. 
In the case of Gecarcinus ruricola (Plate XXVI.), a 
species very common in the West Indies, the migra- 
tion to the sea takes place annually during the 
rainy season in May. The Crabs are described as 
coming down from the hills in vast multitudes, 
clambering over any obstacles in their way, and even 
invading houses, in their march towards the sea. 
Stebbing states that " The noise of their march is 
compared to the rattling of the armour of a regiment 
of cuirassiers." The females enter the sea to wash 
off the eggs which they carry attached to their 
abdominal appendages, or rather, probably, to allow 
the young to hatch out. The Crabs then return 
whence they came, and are followed later by the 
young, which, having passed through their larval 
stages in the sea, leave the water, and are found in 
thousands clinging to the rocks on the shore. 

On Christmas Island, in the Indian Ocean, 
Dr. C. W. Andrews studied the habits of another 
Land Crab, of which the proper name seems to be 
Gecarcoidea lalandii. He says : " This is the com- 
monest of the Land Crabs inhabiting the island, and 
is found in great numbers everywhere, even on the 
higher hills and the more central portion of the 



PLATE XXVI 




A WEST INDIAN" LAND-CRAB, Gecarcintts ruricola. (REDUCED) 




A LAND HERMIT-CRAB, Cifnotita rugosa. (REDUCED) 



CRUSTACEA OF THE LAND 191 

plateau. In many places the soil is honeycombed 
by its burrows, into which it rapidly retreats when 
alarmed. These Crabs seem to feed mainly on dead 
leaves, which they carry in one claw held high over 
the back and drag down into the burrows. From 
their enormous numbers, they must play a great part 
in the destruction of decaying vegetable matter and 
its incorporation into the soil." 

" Once a year, during the rainy season, they descend 
to the sea to deposit [or, rather, to hatch out] their 
eggs, and during this migration hundreds may be 
seen on every path down steep slopes, and many 
descend the cliff-face itself. They remain on the 
beach for a week or two, and . . . afterwards gradually 
make their way back to their accustomed homes." 

In the year of Dr. Andrews' first visit to the 
island (1898) this migration occurred in January. 
On a subsequent visit to the island in" 1908 he 
obtained specimens of a large Megalopa larva (see 
p. 70) which occurred in enormous quantities in 
the sea shortly after the migration, and also of a 
small Crab which appeared in similar numbers at a 
slightly later date. It seems practically certain that 
these larvae and young are those of Gecarcoidealalandii. 
A second species of Land Crab, Cardisoma hirtipes, 
found on Christmas Island, has very different habits 
from the foregoing. Dr. Andrews says of it : " In 
this island, at any rate, this species must be regarded 
as a fresh-water form, and, in fact, when a specimen 






I 9 2 THE LIFE OF CRUSTACEA 

was seen it might be taken as an indication that 
fresh water was not far off. It lives in deep holes in 
the mud at the sides and bottom of the brooks." 
Dr. Andrews tells me that he never saw this species 
at or near the sea (in marked contrast to Gecar- 
coidea), and this agrees with the observations of 
other travellers on species of the genus Cardisoma, so 
that the breeding habits remain unknown. There is 
every probability, however, that in this case, also, the 
young stages are passed in the sea. 

The student will find, in many textbooks on 
zoology, the statement that some Land Crabs of the 
genus Gecarcinus develop without metamorphosis. 
Although it is impossible, with our present know- 
ledge, to state definitely that this is not the case, 
there is absolutely no evidence to support it, and it 
is an interesting example of the way in which 
erroneous statements sometimes gain currency in 
science. 1 It is based upon the fact that in 1835 
Professor J. O. Westwood described the early stages 
of " a West Indian Land Crab," in a paper " On the 
Supposed Existence of Metamorphosis in the Crus- 
tacea," published in the Transactions of the Royal 
Society. Professor Westwood found that the em- 
bryos extracted from the egg possessed all the 
appendages of the adult except the swimmerets, and 
that young specimens clinging to the abdomen of 

1 I am indebted to Mr. J. T. Cunningham for calling my 
attention to some of the facts here recorded. 



CRUSTACEA OF THE LAND 193 

the parent were perfectly-formed little Crabs. The 
specimens which he described were sent to him by 
the Rev. Lansdown Guilding, of St. Vincent, who 
also deals with the subject in a note published in 
the Magazine of Natural History in the same year. 
Neither Westwood nor Guilding refers to the Crab 
as a Gecarcinus, although Guilding calls it the 
" Mountain Crab," a name which Patrick Browne 
in 1756 gives to the Gecarcinus ruricola of Jamaica. 
So far as I am aware, the first writer to refer to 
Westwood's Crab as a Gecarcinus, was Professor 
T. Bell, who in his " British Stalk-eyed Crustacea," 
published in 1853, states that some of the original 
specimens had come into his possession. They con- 
sisted of the detached abdomens of female Crabs, 
with eggs and young adhering to them. It would 
be by no means easy to identify the species of Crab 
to which a detached abdomen belonged, and there 
is nothing in the whole history inconsistent with the 
supposition that these observations really relate to a 
River Crab of the family Potamonidae, of which at 
least one species, Pseudothelphusa dentata, is known to 
occur on the island of St. Vincent. As we have 
already seen, some of these River Crabs are quite as 
much land animals as the Gecarcinidae, and they are 
known to have a direct development. 

The Gecarcinidae possess well-developed gills, but 
in addition the gill chambers are modified for air- 
breathing, as in some other amphibious Crabs 
13 



194 THE LIFE F CRUSTACEA 

(Ocypode, Gelasimus, etc.). Each chamber is capacious 
and vaulted, and the lining membrane is thick and 
richly supplied with bloodvessels, and is folded so as 
to divide off the upper part of the chamber as a sort 
of pocket. 

The Land Hermit Crabs of the family Cceno- 
bitidae are found on the coasts of all tropical seas. 
Like the Gecarcinidae, they visit the sea periodically 
for the purpose of hatching off the eggs, and the 
larval stages are marine. The species of the genus 
Ccenobita (Plate XXVI.) resemble the marine Hermit 
Crabs in general shape, and like them use the shells 
of Gasteropod Molluscs as portable shelters. Where 
shells are scarce, other hollow objects are occasion- 
ally utilized ; for example, large individuals will 
sometimes carry about the shell of a broken coco- 
nut, and a specimen has been seen to walk off in a 
cracked test-tube discarded by a naturalist who was 
investigating their habits. In one instance Pro- 
fessor Alcock saw an individual " so big that it 
seemed to have given up hope of finding a house, and 
was wandering about recklessly, with its tail behind 
it all unprotected." 

The Coenobites often climb into bushes in search 
of food, and Dr. Alcock " once found one of them 
busy, like a large bee, among the florets of a coco- 
nut, which made me wonder whether they may not 
sometimes play a part in fertilizing flowers." They 
are, however, by no means exclusively vegetarians. 









CRUSTACEA OF THE LAND 195 

The author just quoted describes a visit to Pitti 
Bank in the Laccadive Archipelago, the breeding- 
ground of two species of terns. The ground was 
everywhere strewn with the dead bodies and clean- 
picked skeletons of the young birds. " We soon dis- 
covered that one great cause of the wholesale 
destruction of young birds was the voracity of 
swarms of large Hermit Crabs (Coenobite), for again 
and again we found recently killed birds, in all the 
beauty of their first speckled plumage, being torn to 
pieces by a writhing pack of these ghastly Crus- 
taceans. There were plenty of large Ocypode Crabs, 
too (0. ceratophthalmus), aiding in the carnage." 

On Christmas Island Dr. Andrews found a species 
of Ccenobita not unfrequently in the higher parts of 
the island far from the sea, and he remarks that the 
occurrence of large marine shells high up on the 
hills seemed very puzzling until it was noticed that 
they were brought by the Hermit Crabs. 

The species of Ccenobita possess a very curious 
adaptation for aerial respiration. The soft skin of 
the abdomen is traversed by a network of blood- 
vessels and acts as a kind of lung, and a pair of 
contractile vesicles at the base of the abdomen serve 
as accessory hearts in promoting a specially active 
circulation in that part of the body. The lining 
membrane of the gill chambers also appears to aid in 
respiration as in other terrestrial Decapods. 

The " Robber Crab " or " Coconut Crab " (Birgus 



196 THE LIFE OF CRUSTACEA 

latro Plate XXVII.) also belongs to the family 
Ccenobitidae, and has attracted much notice from its 
relatively gigantic size and its singular habits. Al- 
though resembling Ccenobita closely in essential 
structure, Birgus differs from it and from most other 
Hermit Crabs in not making use of a portable 
shelter, perhaps owing to the difficulty of obtaining 
one of suitable size. The necessary protection for 
the abdomen is obtained by a redevelopment of he 
shelly plates (terga) on the upper surface of the 
abdominal somites. The abdomen is carried doubled 
underneath the body to protect the soft under- 
surface, and the animal, when threatened, seeks a 
shelter for its vulnerable hinder part in the nearest 
hole or cranny. The swimmerets are absent in the 
male sex, and are present only on one side of 
the abdomen in the female. This unsymmetrical 
development of the appendages is interesting as 
indicating the derivation of the Robber Crab from 
ancestors adapted to living in the unsymmetrical 
shells of Gasteropod Molluscs. The last pair of 
abdominal appendages, which in other Hermit 
Crabs serve to hold the body in the shell, are here 
much reduced in size, and quite useless for that 
purpose. The carapace is very broad posteriorly, 
owing to the great development of the branchial 
cavities, which are much too capacious for the very 
small gills. As in the true Land Crabs, the lining 
membrane of the gill cavity is thick and spongy, and 



PLATE XX I'll 




THE COCO-NUT CRAB, Birgus latro. (MUCH REDUCED) 



CRUSTACEA OF THE LAND 197 

traversed by numerous bloodvessels ; but in this case 
its efficiency as a lung is added to by numerous 
tufted papillae, which increase the surface exposed 
to the air. 

As in other Hermit Crabs, the last two pairs of 
legs are shorter than the others, and they end in 
small chelae. The last pair are very slender, and are 
usually carried folded up within the gill chambers, 
which they possibly serve to keep clear from foreign 
bodies. The penultimate pair of legs are stouter, 
and the two pairs in front of these are long walking 
legs. The chelipeds are very strong and are of un- 
equal size. When attacked, the animal defends 
itself, not, as might have been expected, with its 
chelipeds, but with the first pair of walking legs, the 
sharp points of which form very efficient weapons. 

The statement that the Robber Crab climbs lofty 
trees was first made by the Dutch naturalist 
Rumphius, in the beginning of the eighteenth 
century. Its accuracy has been often doubted or 
denied since then, and only finally put beyond 
dispute by a photograph taken on Christmas Island 
by Dr. Andrews, which shows one of these Crabs in 
the act of descending the trunk of a sago-palm. It 
seems not impossible that the habits of the animal 
may vary to some extent in different localities, and 
that where food is abundant on the ground the tree- 
climbing habit may be in abeyance. If this were so, 
it would explain the very definite statements made 



198 THE LIFE OF CRUSTACEA 

by some observers, that Birgus does not climb 
trees. 

In localities where coconut palms abound, Birgus 
feeds largely on the nuts, tearing off the fibrous outer 
husk and breaking open the shell by hammering 
with its powerful claws at one of the " eye-holes." 
According to Darwin in his " Naturalist's Voyage," 
the pincers of the penultimate pair of legs are used 
for extracting the contents of the nut, but this 
observation does not seem to have been confirmed. 
In spite of its name of " Coconut Crab," however, 
Birgus by no means feeds exclusively on coconuts. 
On Christmas Island, where until recently there 
were no coconut palms, the Crabs are exceedingly 
abundant, and, according to Dr. Andrews, they " eat 
fruits, the pith of the sago-palm and the screw-pines, 
dead rats and other carrion, and any of their fellows 
that may have been injured. . . . They are excellent 
scavengers, and have a curious habit of often drag- 
ging their food long distances before attempting to 
eat it. I have seen a Crab laboriously pulling a 
bird's wing up the first inland cliff, half a mile or 
more from the camp whence it had stolen it." 

Large specimens of the Robber Crab may be at 
least a foot in length of body when the abdomen is 
straightened out. Their great strength is illustrated 
by the fact, related by Darwin, that specimens 
placed in'a strong biscuit-tin, of which the lid was 
secured by wire, escaped by turning down the edges 



CRUSTACEA OF THE LAND 199 

with their claws, and in doing so actually punched 
holes quite through the tin. 

The breeding habits and mode of development of 
the Robber Crab have often formed the subject of 
inquiry by naturalists, but it is only recently that 
Dr. Willey has been able to prove definitely that the 
female visits the sea for the purpose of hatching off 
the eggs, and that the young are hatched in the zoe'a 
stage. The larvae obtained by Dr. Willey have been 
described by Mr. Borradaile, who finds that, as was 
to be expected, they closely resemble those of 
Ccenobita. There appears, however, to be no such 
simultaneous migration of the Crabs towards the sea 
as has been described in the case of the Gecarcinidae. 
The statement, quoted by Darwin, that Birgus visits 
the sea every night for the purpose of moistening its 
branchiae, cannot be universally applicable, since the 
Crabs are often found, as on Christmas Island, at 
distances from the sea which put a nightly journey 
to it out of the question. 

Of all Crustacea, the most completely adapted to 
terrestrial life are the Land Isopods, or Woodlice, 
which may be found in every garden. It is true 
that most species are found in damp places, although 
some that inhabit the sandy deserts of Asia and 
Africa must be content with a very slight degree of 
humidity ; and in no case is their dependence on 
moisture greater than, for instance, that of many 
Insects and Arachnids which are regarded as typically 



200 THE LIFE OF CRUSTACEA 

terrestrial animals. Since there is reason to believe 
that the Woodlice have been derived from marine 
ancestors they show no special affinities to the 
fresh-water Isopoda, like Asellus it is interesting to 
find that the most primitive forms, which have de- 
parted least from the general Isopod type, are 
commonly found on or near the seashore. The 




FIG. 63 THE SEA-SLATER (Ligia oceanica). ABOUT TWICE 
NATURAL SIZE. (After Sars.) 

" Sea-slater," Ligia oceanica (Fig. 63), which is 
abundant in rocky places on our own coast, is one 
of the most primitive forms. It has a broad, flat- 
tened, greenish-brown body, about an inch long, and 
it runs quickly, creeping into narrow crevices of the 
rocks, so that it is not easy to catch. The anten- 
nules, as in the other land Isopods, are very minute, 
but the antennae are long, and have, besides the five 



CRUSTACEA OF THE LAND 201 

segments which form the " peduncle," a " flagellum " 
of about twelve short segments. The uropods or 
tail appendages are long, each with two slender, 
pointed branches. On the under - side of the 
abdomen can be seen the five pairs of pleopods, each 
with two plate-like branches attached to a very short 
peduncle. As in most aquatic Isopods, the plates of 
the pleopods are soft and thin, and appear adapted 
to act as gills, although the outer plate of each pair 
is somewhat stiffer than the inner. The Sea-slater 
is generally found just above high-water mark, prob- 
ably always within reach of the salt spray, and it is 
said sometimes to enter the water of rock-pools. 

In almost every garden there may be found, under 
flower-pots and the like, a Woodlouse, about two- 
thirds of an inch long, of a brown colour, with 
yellowish blotches arranged in a row on each side of 
the back. This is Oniscus asellus, a species widely 
distributed in Europe and North America. It has 
the antennae shorter than in Ligia, and the flagellum 
is composed of only three segments. The uropods 
are quite short. The endopodites of the pleopods 
are membranous gill-plates, which serve for respira- 
tion in the moist air in which these animals generally 
live. The exopodites are stiff plates which cover and 
protect the delicate endopodites ; it is probable that 
they also aid in respiration, for they contain a 
system of minute channels, filled with air, where the 
cuticle is separated from the underlying cells. As 



202 



THE LIFE OF CRUSTACEA 



these channels are nowhere open to the outside, the 
air must find its way in by diffusion through the 
cuticle. 

Even more abundant than Oniscus asellus, and 
often found together with it, is Porcellio scaber (see 
Fig. 20, p. 51). It is usually of a dark bluish-grey, 
but occasionally it is irregularly mottled with a 




FIG. 64 STRUCTURE OF THE BREATHING ORGANS OF Porcellio scaber. 
(From Lankester's "Treatise on Zoology," after Stoller.) 

A, Exopodite of first pleopod, showing the tuft of air-tubes 
("pseudo-tracheae"), seen through the transparent cuticle; B, 
vertical section through same ; C, part of section more highly 
magnified, art, Point of attachment of exopodite to peduncle ; 
c, cuticle; gr, grooved area of cuticle ; hy, hypodermis, or layer 
of cells under the cuticle ; n, nucleus of hypodermis cell of air- 
tube ; o, external opening ; tr, air-tubes 

lighter colour. The flagellum of the antenna has 
only two segments. The most interesting difference 
from Oniscus, however, is found in the pleopods. If 
the under-side of the living animal be examined with 
a pocket lens, a white spot will be seen on each 



CRUSTACEA OF THE LAND 



203 



exopodite of the first two pairs of pleopods. When 
the structure of the pleopods is investigated by 
means of microscopic sections (Fig. 64), it is found 
that the white spots are tufts of fine branching tubes 
radiating into the interior of the exopodite from a slit- 
like opening on the outer edge. These tubes arise by 
an in-pushing of the integu- 
ment, and they are lined 
throughout by a delicate con- 
tinuation of the external cuticle. 
During life they are filled with 
air, and they serve to aerate the 
blood circulating in the interior 
of the appendage. 

Another Woodlouse common 
England is Armadillidium 




FIG. 65 Armadillidium 
vulgare. x -2.\. (After 
Sars.) 



in 

vulgar e (Fig. 65), a little slaty- 
grey species with a very con- 
vex body, which rolls itself 
into a ball when touched. Like the last-mentioned 
species, it has two segments in the flagellum of its 
short antennae, and it has tufted air-tubes in the 
exopodites of the first two pairs of pleopods. It is 
often mistaken for an animal of widely different 
structure, which it superficially resembles the Pill 
Millipede (Glomeris marginata). The latter, however, 
may easily be recognized by having either seventeen 
or nineteen pairs of walking legs (instead of seven 
pairs), set close together in the middle line of the 



204 THE LIFE OF CRUSTACEA 

body, and by lacking the plate-like pleopods. The 
resemblance between the two animals can hardly be 
regarded as a case of " mimicry," since there is no 
reason to believe that either benefits by its likeness 
to the other. As in so many other cases of " con- 
vergent resemblance " between animals of different 
structure, it does not seem possible to get beyond 
the vague suggestion that a similarity in habits may 
have led, in some way that we do not understand, to 
a similarity in appearance. 

The presence of air-tubes in the pleopods of many 
Woodlice raises some questions which are of impor- 
tance with reference to the classification of the 
Arthropoda as a whole. The Six-legged Insects, 
most Spiders and many of their allies, the Centi- 
pedes and Millipedes, and the worm-like Peripatus, 
all breathe air by means of fine tubes which pene- 
trate throughout the body, and bring the air into 
close contact with the tissues. These tubes, which 
are known as "tracheae," arise as ingrowths of the 
outer layer of the embryo, and are lined by a delicate 
continuation of the external cuticle. It has been 
held by some zoologists that so peculiar a system of 
breathing organs must indicate a common descent 
of the animals that possess them, and accordingly 
it has been proposed to separate the Insects, Arach- 
nids, Myriopods, and Peripatus, as a group, Tracheata, 
from the Crustacea and some other Arthropods which 
have no tracheae. The air-tubes of the Woodlice, 



CRUSTACEA OF THE LAND 205 

however, are precisely like tracheae in structure 
and function, and only differ from the tracheae 
of the other groups in the fact that they are 
confined to the appendages, and do not penetrate 
into the body. Since the Woodlice are a small and 
highly specialized branch of the Crustacea, we can 
hardly suppose that they derive their tracheae from 
any ancestral type which they had in common with 
the widely different Arachnids, for example ; and if 
tracheae have been evolved independently in these 
two groups, there seems no reason why those of the 
Insects may not have arisen independently of either. 
This is only one example out of many which go to 
show that, in attempting to reconstruct the genealogy, 
or phylogeny, as it is called, of the animal kingdom, 
we must constantly admit the possibility of " con- 
vergent evolution." 

Although Woodlice are very common animals, com- 
paratively little is known of their habits. They 
seem to live chiefly on vegetable food, and sometimes 
damage seedlings and tender plants in gardens and 
greenhouses, but occasionally they are carnivorous, 
and even cannibalistic, in their habits. A few species 
live as " guests " in ants' nests, and one of these, 
the little blind white Platyarthrus hoffmannseggii, is 
common in many localities in this country. Why 
the ants tolerate their presence we do not know, 
for they do not seem to render any service to their 
hosts, as do the plant-lice and some other insects 



206 THE LIFE OF CRUSTACEA 

that are kept by the ants for the sake of the secre- 
tions which they yield. 

The Woodlice, like some other Isopoda, have a 
peculiar method of moulting. Instead of the whole 
exoskeleton being cast off at one time, as in other 
Crustacea, that of the hinder half of the body is 
moulted first, and it is only after two or three days, 
when the new cuticle has hardened, that the exo- 
skeleton of the anterior half follows. As a result of 
this arrangement, it occasionally happens that speci- 
mens are found with the fore part of the body differing 
in colour from the hind part, owing to the one having 
been moulted more recently than the other. 

Woodlice occur in most regions of the globe, 
and one of the most remarkable features of their 
geographical distribution is the extremely wide 
range of certain species. This is probably due, 
at least in many cases, to their accidental transport 
by human agency. Thus, Porcellio scaber, so common 
in this country, is also found in great abundance in 
New Zealand ; but Professor Chilton notes that it 
is usually found near buildings, and only rarely in 
the native bush, so that there can be no doubt that 
it has been introduced by artificial means. 



CHAPTER X 
CRUSTACEA AS PARASITES AND MESSMATES 

THE life of every animal is in more or less 
intimate relation with that of all the living 
creatures which surround it. Some serve for its 
food, or supply it with shelter or foothold ; others 
prey upon it, or compete with it for the necessaries 
of life; and others, again, influence it for good or 
evil in countless ways more subtle than these, but 
equally important. There are some associations 01 
a closer and more enduring nature, to which the 
names of Symbiosis, Commensalism, and Parasitism, 
are applied, and it is with examples of these that 
the present chapter is concerned. 

The term Symbiosis is strictly applied to an inti- 
mate physiological partnership, such as we find in 
some of the lower animals and plants, and in this sense 
there are no truly symbiotic Crustacea. The word, 
however, is sometimes used, in its literal sense of a 
"living together," to embrace all cases of animals 
living together for mutual advantage. Commen- 
salism means, literally, " sitting at the same table," 

207 



2o8 THE LIFE OF CRUSTACEA 

and ought to be applied only to cases where two 
or more animals, living together as " messmates," 
partake of the same food ; but it is sometimes used 
more loosely to include instances where one of the 
animals does not actually share in the food-supply 
of the other. Parasitism, again, implies that the 
parasite lives permanently at the expense of its host, 
by sucking its juices or otherwise, and in this case 
also there are innumerable degrees and varieties of 
dependence, which defy inclusion in a strictly logical 
scheme of classification. Even such typical parasites 
as Tape-worms, for example, might strictly be regarded 
as commensals, sharing in the host's food only after 
it has entered the alimentary canal. Finally, in all 
these kinds of interrelation, we find cases where 
the association is temporary, intermittent, or almost 
accidental, and where there are no perceptible 
adaptations of structure directed to its maintenance 
in either of the partners. From these we may trace 
a series of gradations leading to cases where the 
associated organisms are never found apart, and 
where the structure of both is profoundly modified 
in adaptation to the particular form of association. 

Perhaps the simplest form of association between 
two animals is found where one utilizes the other 
as a means of transport. The little Gulf- weed Crab, 
previously mentioned, is very often found clinging to 
the carapace or skin of large marine turtles. It is 
not a parasite, since it can hardly derive any food 



PLATE XXV11 




o s 
- - 



PARASITES AND MESSMATES 209 

from the Turtle itself; neither is it a commensal, 
for there is no evidence that it shares in the Turtle's 
meals. It probably takes to a Turtle, when it can 
find one, as giving it a wider range of operations than 
is afforded by its usual drift-log or tuft of sargasso- 
weed. A somewhat similar case is afforded by some 
of the Barnacles that are found on the skin of 
Whales. The species of Conchoderma, for instance, 
are often found on certain Whales, but they may 
also occur on inanimate floating objects. Other 
Whale-infesting Cirripedes, however, are specially 
adapted to their habitat, and never occur elsewhere. 
For example, Coronula (Plate XXVIII.) is a genus 
of sessile Barnacles in which the shell is elaborately 
folded, forming a series of chambers into which pro- 
longations of the Whale's epidermis grow, securely 
fixing the shell. Tubicinella is even more effectively 
protected against dislodgment, for its shell is sunk 
in the thickness of the Whale's skin, with only the 
opening exposed. Other genera of sessile Barnacles 
(Chelonobia, etc.) are found adhering to the shell of 
Turtles. The increased food-supply made available 
by the host's movements through the water is 
probably the chief advantage that the Barnacles 
gain in such cases. This is indicated by the fact 
that certain small stalked Barnacles (Dichelaspis, etc.), 
found on large Crabs and Lobsters in tropical seas, 
generally cluster on the mouth parts of their hosts, 
near the entrances to, or even within, the gill 
14 



210 THE LIFE OF CRUSTACEA 

chambers, profiting no doubt by the respiratory 
currents and the food particles they carry. 

A great variety of Crustacea find shelter and 
defence in association with Sponges, Corals, and 
other more or less sedentary animals. Sponges are 
not eaten by many marine animals, the needle-like 
spicules which often form their skeleton no doubt 
helping to render them distasteful, and many small 
Crustacea, Amphipods, Isopods, Prawns, etc., profit 
by their immunity from attack, and take up their 
abode in the internal channels and cavities of the 
Sponge. The beautiful siliceous Sponge known as 
" Venus's Flower-basket " (Euplectella) very often 
contains imprisoned within it specimens of a delicate 
little Prawn (Spongicola venusta) or of an Isopod 
(JEga spongiophila). As these Crustacea share with 
the Sponge the food particles drawn in by the currents 
of water passing through the pores in its walls, they 
are in the strict sense commensals. 

The Corals and various other animal organisms 
commonly known as " Zoophytes," forming together 
with the Jellyfishes the group Ccelentera, are very 
effectively protected against the attacks of most 
predatory animals by the possession of " stinging 
cells/' and this protection is shared by many other 
animals which shelter among them. Thus, the 
branching Coral stocks which grow in great luxuri- 
ance on tropical coasts support a rich and varied 
assemblage of animals, some of which may actually 



PARASITES AND MESSMATES 



211 



prey upon the Coral polypes, but all of which profit 
by the fact that few enemies venture to pursue them 
in their retreats. Innumerable prawn-like animals 
of the Alpheidae and other families, and many kinds 
of Crabs, are found among living Corals. The Crabs 
of the family Trapeziidas are especially characteristic 
of such habitats, and their thin, flat bodies seem to 
be adapted to slip into slits and crannies of the Coral 
blocks. The most highly specialized of all Coral 




FIG. 66 Two BRANCHES OF A CORAL (Seriatopora) SHOWING 
"GALLS" INHABITED BY THE CRAB Hapalocarcinus marsupialis. 
ON THE RIGHT THE FEMALE CRAB, EXTRACTED FROM THE GALL 
AND FURTHER ENLARGED 

Crabs, however, are the species of the family Hapalo- 
carcinidae, which modify in various ways the growth 
of the corals on which they live. In some of the 
more delicately branched kinds of Coral there may 
sometimes be found hollow bulbous growths, each of 
which contains imprisoned within it a little Crab 
Hapalocarcinus marsupialis (Fig. 66). It seems that 
the female Crab (the habits of the male are not 
definitely known) settles down among the branches 



212 THE LIFE OF CRUSTACEA 

of the Coral, and that the irritation of its presence 
causes the branches to grow up and surround it, 
coalescing with each other to form a kind of cage, 
and ultimately leaving only one or two small open- 
ings. Through these openings water can enter to 
enable the Crab to breathe, and no doubt food 
particles find their way in, but it is not possible for 
the Crab to leave its prison. The production of 
these abnormal growths of the Coral is closely 
analogous to the formation of " galls " on plants as 
a result of the irritation set up by the presence of 
insect larvae or other parasites, and it is not inappro- 
priate, therefore, to speak of them as " Coral galls." 

The Medusae, or Jellyfishes, like other Crelentera, 
are provided with poisonous stinging cells, which, in 
the larger species of our own seas, are powerful 
enough to cause discomfort to bathers who come in 
contact with them. The protection thus afforded is 
no doubt of advantage to the little globular Amphi- 
pods of the genus Hyperia (Fig. 67), which are almost 
always to be found sheltering under the bells of the 
larger Medusae. In what way the Amphipods escape 
injury from the stinging cells of their host is not 
known. 

In all the cases mentioned, the advantages of the 
partnership seem to be all on one side, but there 
are numerous instances in which both partners seem 
to reap some benefit. A species of Hermit Crab very 
common in moderately deep water on many parts of 



PARASITES AND MESSMATES 



213 




the British coasts, Eupagurus pridcauxi, is always 
found to have a Sea-anemone (Adamsia palliata) 
attached to the shell which it carries. The Anemone 
has a broad base which is wrapped round the shell, 
the mouth, surrounded by the tentacles, being on the 
under-side next the opening of the shell. There 
seems no reason to doubt 
that the presence of the 
Anemone does afford some 
degree of protection to the 
Hermit, and that, on the 
other hand, the Anemone 
benefits by being carried 
about, and shares in the 
crumbs from the Hermit's 
meals. It is stated that, 
when the Hermit removes to 

a new shell, it detaches the Anemone from the old 
shell with its pincers and places it in position on the 
new one. It appears, however, that it is not always 
necessary for the Hermit to remove to a larger shell 
as it grows, for the enveloping Anemone, as it in- 
creases in size, extends beyond the mouth of the 
shell, and so enlarges the shelter. Further, the 
Anemone in course of time dissolves the shell almost 
entirely away, and the Hermit is enveloped only by 
the soft fleshy mantle which it forms. 

In a similar way the deep-sea Hermit Crab Para- 
pagurus pilosimanus (see Plate XVI.) is always found 



FIG. 67 Hyperia galba, 
FEMALE. ENLARGED. 
(After Sars.) 



214 THE LIFE OF CRUSTACEA 

lodged in a fleshy mass formed by a colony of Sea- 
amenones (Epizoanthus) , within which, when it is 
cut open, may be found the remains of the shell 
which the Hermit first inhabited. A further develop- 
ment of the same habit is given by Paguropsis typica, 
found in deep water in Indian seas, which does not 
inhabit a shell at any time, but carries a fleshy 
blanket formed by a colony of Anemones. 

In dredging off the British coasts, we often find 
smooth rounded lumps of a Sponge (Suberites ficus), 
generally yellowish-grey in colour, having a round 
opening in which the claws of a small Hermit Crab 
(Eupagurus cuanensis) may be seen. On cutting open 
the Sponge, the body of the Hermit is seen to be 
lodged in a spiral cavity, and at the apex may be 
found the remains of a shell that has been corroded 
away by the Sponge which settled on and replaced 
it. Other species of Hermit Crabs constantly have 
their shells covered with a horny crust formed by 
Hydroid zoophytes (Hydractinia, etc.), and in this 
case also the extension of the Hydroid colony beyond 
the lip of the shell relieves the Hermit from the 
necessity of so frequently changing to a larger shell 
as it grows. 

A number of other animals are found associated 
with Hermit Crabs, without, as far as we can see, 
rendering any service in return for the house-room. 
The Whelk-shells inhabited by Eupagurus bernhar- 
dus (see Plate VII.) often contain one of the bristle- 



PARASITES AND MESSMATES 215 

footed worms (Nereilepas fucata), which may some- 
times be observed to protrude its head from the 
shell when the Crab is feeding, and to snatch away 
fragments of the prey from the very jaws of its host. 
It is thus, in the strict sense of the word, a com- 
mensal. Species of Copepods, Amphipods, Porce- 
lain Crabs, and even a Mysid, have been found 
sharing the lodging of Hermit Crabs in a similar 
way, and in addition there are various parasites, 
presently to be mentioned, found on the Crabs 
themselves, so that each Crab forms the centre of a 
whole community of widely diverse organisms all 
more or less directly dependent on it. 

A habit similar to those of some Hermit Crabs is 
that of the Crab Dromia (see Plate IX.), mentioned 
in a previous chapter, which carries, as a cloak, 
a mass of living sponge, holding it in position by 
means of the last two pairs of legs. Even the 
" masking " habit of the Spider Crabs, already 
described (p. 96), may be regarded as a kind of 
symbiosis, since the sponges, zoophytes, etc., which 
grow on the Crabs no doubt benefit by being carried 
about in return far the protection they give. 

One of the strapgest habits is that of certain little 
tropical Crabs, of which Melia tessellata (Fig. 68) is 
the best known, which carry in each claw a living 
Sea-anemone and use it as a weapon. The claws or 
chelipeds are in this case of small size, so that they 
woud be of little use by themselves for attack or 



2l6 



THE LIFE OF CRUSTACEA 



defence ; but the fingers are provided with recurved 
teeth, enabling them to take a firm hold of the 
slippery body of the Anemone. Particles of food 
caught by the tentacles of the Anemone are removed 
and eaten by the Crab, which uses for the purpose 
the long walking legs of the first pair. The same 
limbs are also used in the process of detaching the 




FIG. 68 A, THE CRAB Melia tessellata CLINGING TO A BRANCH 
OF CORAL, AND CARRYING IN EACH CLAW A LIVING SEA- 
ANEMONE ; B, ONE OF THE CLAWS FURTHER ENLARGED TO 

SHOW THE WAY IN WHICH THE ANEMONE IS HELD. (After 

Borradaile.) 

Anemones from the stone on which they may be 
growing. The Anemones do not appear to suffer 
from the rough treatment to which they are sub- 
jected, but whether they can reap any benefit from 
the partnership is very doubtful. 

From remote antiquity it has been known that a 
little Crab (Fig. 69) is frequently found living within 



PARASITES AND MESSMATES 217 

the shells of bivalve Molluscs, such as Oysters, Mus- 
sels, and especially the large mussel-like Pinna, which 
is common in the Mediterranean. Ancient writers 
regarded this as a case of association for mutual 
advantage, believing that the Pinnotheres warned the 
Pinna of the approach of enemies or of the entrance 
of prey between its gaping valves. It is even stated 
that the Pinna and Crab were depicted in Egyptian 
hieroglyphics to symbolize the dependence of a man 
on his friends. 

As a matter of fact, however, there is no reason to 




FIG. 69 THE COMMON PEA CRAB (Pinnotheres pisum), FEMALE. 
NATURAL SIZE. 

believe that the Molluscs which harbour species of 
Pinnotheres and allied genera benefit in any way by 
the presence of the Crabs. The latter probably feed, 
as their hosts do, on particles brought in by the 
current of water entering the mantle cavity. They 
are therefore strictly " commensals," though it is 
usual, and perhaps equally correct, to speak of them 
as " parasites." The case is, indeed, an example of 
the difficulty of defining these two terms. At all 
events, the Pinnotherid Crabs show one of the 
characteristics of parasites in being to some extent 



218 THE LIFE OF CRUSTACEA 

degenerate in their structure. The carapace and the 
rest of the exoskeleton, no longer needed for protec- 
tion, have become soft and membranous, and the eyes 
and antennules. the chief organs of sense, are very 
minute. As in many parasites, also, the eggs pro- 
duced by the female are very numerous, and the 
abdomen is very broad and deeply hollowed for their 
reception. 

While most of the Pinnotheridae live in bivalve 
Molluscs, some species are associated with other 
invertebrate animals. Pinnaxodes chilensis is found 
in a species of Sea-urchin (Strongylocentrotus gibbosus) 
on the coast of Chili. On opening the shell of the 
Urchin, the Crab is found enclosed in a thin-walled 
bag formed by enlargement of the terminal part of 
the host's intestine. 

It did not escape the notice of Aristotle that a 
little Shrimp sometimes occurred in the Pinna in 
place of the Crab. This is Pontonia custos, and other 
species of the same and allied genera have similar 
habits. 

The order Isopoda includes a very large number 
of parasitic species. The extensive family Cymo- 
thoidae presents a whole series of gradations in 
habits and structure between actively swimming 
predatory species and others which in the adult 
state are permanently fixed to their host, usually a 
fish, and are incapable of movement. At one end of 
the series are the species of Cirolana,' which have 



PARASITES AND MESSMATES 



219 



powerful biting jaws. Of C. borealis (Fig. 70), Mr. 
Stebbing remarks that " it is a good swimmer, tena- 
cious of life, a savage devourer of fish, and not to be 
held in the human hand with impunity." The species 
is not uncommon in British seas, and numerous indi- 
viduals will sometimes 
attack a Cod or other 
large fish, perhaps after 
it has been caught on a 
hook, and gnaw their 
way into its body, so 
that when brought to 
the surface the fish con- 
sists of little more than 
skin and bone. 

The little Eurydice 
achatus, belonging to 
the same subfamily, 
Cirolaninse, is com- 
monly taken in the 
tow-net in sandy bays on our own coasts. It is said 
sometimes to attack bathers, and to " nip most 
unpleasantly." 

More definitely parasitic are the species of Mga 
and allied genera, which have piercing and suctorial 
mouth parts, and suck the blood of fish. They are 
usually found adhering closely to the skin of their 
victim by means of the strong hooked claws of the 
anterior pairs of legs ; but they have not lost the 




FIG. 70 Cirolana borealis. 
TWICE NATURAL SIZE. 
Sars.) 



ABOUT 
(After 



220 THE LIFE OF CRUSTACEA 

power of locomotion, and, as females bearing eggs 
are never taken on fish, it would appear that they 
drop off after gorging themselves with blood, and 
probably seek a retreat at the bottom of the sea, 
where they may hatch their young in safety. The 
digestive canal of JEga dilates into a large bag, 
which becomes distended with a semi-solid mass of 
blood. This mass, when extracted and dried, is the 
" Peter's stone " of old Icelandic folklore, to which 
magical and medicinal virtues were attributed. The 
species JEga spongiophila, already mentioned, differs 
in its habits from all the other species of the genus, 
since it lives, not on fish, but in the interior of a 
sponge. 

The most completely parasitic members of the 
Cymothoidae are found in the subfamily Cymo- 
thoinae, including the typical genus Cymothoa 
(Plate XXIX.) and many others. The adult animals 
are found clinging to the skin of fishes, the legs 
being provided with strong hook-like claws that give 
them a very firm hold. Some species, especially 
common on Flying-fishes, cling to the tongue of the 
fish, and almost prevent it from closing its mouth. 
When young, the Cymothoinae swim freely, and the 
shape of the body is not unlike that of the Ciro- 
laninse ; but after they have settled on a host the 
body often becomes distorted and unsymmetrical. 
A still more remarkable change occurs in the repro- 
ductive organs in some, if not in all members of this 



PLATE XXIX 




Cymothoa oestrum, AN ISOPOD PARASITE OF FISH 
(SLIGHTLY ENLARGED) 




Sacculina carcini ATTACHED UNDER THE ABDOMEN OF A COMMON SHORE-CRAB 
(REDUCED) 



PARASITES AND MESSMATES 221 

subfamily. Each individual, when it first attaches 
itself to a host, presents the characters of the male 
sex. Later it becomes a female, develops a brood- 
pouch, and produces eggs. The animals are, in fact, 
hermaphrodite ; but it is to be noted that the 
hermaphroditism is of a different kind from that 
presented by the Cirripedia, since the organs of 
the two sexes are successively, not simultaneously, 
developed. Where, as in this case, the male phase 
comes first in the life-history of the individual, the 
condition is known as " protandrous " hermaphro- 
ditism. 

Another large group of parasitic Isopods is the 
suborder Epicaridea, all the species of which are 
parasitic on other Crustacea. It is not uncommon 
to find specimens of the common Prawn (Leander 
serratus) which have a large swelling on one side 
of the carapace. If the lower edge of the carapace 
be raised, it will be seen that this swelling is due to 
the presence in the gill cavity of an Isopod parasite 
(Bopyrus squillarum). A closely similar form, found 
on Prawns of the genus Spirontocaris, is Bopyroides 
hippolytes, represented in Fig. 71. Other allied 
species are found on Hermit Crabs and other 
Decapods. When extracted, the parasite is seen 
to have a flat and curiously distorted body, with 
extremely short legs ending in hooked claws. The 
under-side is generally occupied by a relatively 
enormous mass of eggs, which is only partly covered 



222 THE LIFE OF CRUSTACEA 

in by the small brood-plates. The mouth parts form 
a short piercing beak with which the parasite sucks 
the blood of its host. On the under-side of the 
abdomen may usually be found the minute male, 
attached, like a secondary parasite, to the body of 
the female. 

The species of Epicaridea are very numerous, and 
they infest Crustacea belonging to nearly all the 





FIG. 71 A, FRONT PART OF BODY OF A PRAWN (Spirontocaris 
polaris), FROM ABOVE, SHOWING ON THE RIGHT SIDE A SWELLING 
OF THE CARAPACE CAUSED BY THE PRESENCE OF THE PARASITE 
Bopyroides hippolytes IN THE GILL CHAMBER ; B, THE FEMALE 
PARASITE EXTRACTED AND FURTHER ENLARGED ; C, THE MALE 
PARASITE ON SAME SCALE AS THE FEMALE. (After Sars.) 

chief groups of the class, a few even being parasitic 
on other Epicaridea. Many of them differ greatly 
from the Bopyrus just described, and in some cases 
it would be impossible to guess from the structure of 
the adult animals that they were Isopoda, or even 
Crustacea at all. The life-history is not yet com- 



PARASITES AND MESSMATES 223 

pletely known. When hatched from the egg, the 
free-swimming larvae have a short and broad body, 
and, as in other Isopod larvae, have only six instead 
of seven pairs of legs. A later larval stage, just 
before attachment to the final host, has a long 
narrow body and the full number of legs. It has 
lately been shown, however, that, in all probability, 
between these two free-swimming stages there inter- 
venes a stage in which the larvae is temporarily 
parasitic on certain Copepoda. Further, some of the 
Epicaridea, like the Cymothoinae described above, 
are protandrous hermaphrodites, developing the male 
organs when in the last larval stage, and passing 
into the female phase after they have become attached 
to the host. In Bopyrus and many other genera, 
however, there is no evidence that the males ever 
develop into females. 

Some of the most remarkable Epicaridea are those 
belonging to the family Entoniscidae, which are para- 
sitic on Crabs. In these the parasite penetrates from 
the gill chamber into the interior of the body of the 
host, remaining enveloped, however, by a delicate 
membrane which grows in with it from the wall of 
the gill chamber. The body is distorted in an extra- 
ordinary fashion, so that at first sight it seems 
impossible to trace any resemblance to the form of 
a typical Isopod. 

Among the Amphipoda there are a few species be- 
longing to various families of the Gammaridea which 



224 THE LIFE OF CRUSTACEA 

have suctorial mouth parts, and lead a semi-parasitic 
existence ; but the only completely parasitic forms 
are the Whale-lice, forming the family Cyamidae (see 
Fig. 23, p. 55) in the suborder Caprellidea. Although 
differing greatly in the broad, flattened shape of the 
body from the slender, thread-like Caprellidse, they 
closely resemble them in structure, particularly in 
having the abdomen reduced to a mere knob. The 
fourth and fifth pairs of thoracic limbs have dis- 
appeared, although the gills corresponding to them 
are very large ; and the last three pairs of legs have 
long curved claws which enable the Whale-louse to 
cling firmly to the skin of its host. The mouth parts 
are adapted for biting, not for sucking blood, and 
the animals seem to live by gnawing the skin of the 
Whales. In one respect the Whale-lice are unique 
among Crustacean parasites : they have not the 
power of swimming at any period of their life-history. 
The young settle down near their parents, and masses 
of many hundred individuals of all sizes are found 
clinging close together on the skin of the host. 

No group of Crustacea exhibits more numerous or 
more varied examples of parasitism than the Co- 
pepoda. Every grade of transition between a free 
predatory habit of life and the most complete 
dependence upon a host may be traced in various 
families of the subclass. Only a few examples can 
be mentioned here. 

The commonest " fish-lice " are the numerous 



PARASITES AND MESSMATES 225 

species of the family Caligidse, many of which, 
belonging to the genera Caligus (Fig. 72), Lepe- 
ophthirus, etc., are found on marine fishes on our 
own coasts. In these the body is broad and flat, 
but in many of them the resemblance, even in 
general form, . to the free- 
living Copepoda is easily 
traceable. The maxillipeds 
form powerful hooked claws, 
by means of which the ani- 
mals cling to the skin of the 
fish they infest, and in Caligus 
the basal segments of the 
antennules have a pair of 
suckers which aid in ad- 
hesion. The mouth parts 
are adapted for piercing, and 
are enclosed in a suctorial 
proboscis. 

When the young Caligid, 
after passing through the 
free-swimming larval stages, FIG- 72 A FISH-LOUSE 

(Caligus rapax), FEMALE. 

first becomes attached to a x 5. (After Wilson.) 
fish, it adheres by means of a 

thread-like process issuing from the front of the head, 
and formed by the secretion of a gland. At this 
stage, formerly described as an independent species 
under the generic name of Chalimus, the parasite is 
unable to detach itself from its host ; but later, in 
15 




226 



THE LIFE OF CRUSTACEA 



many species, it re-acquires the power of swimming, 
and specimens of Caligus, for instance, are commonly 
found free in tow-net gatherings. 

D 








FIG. 73 STAGES OF DEVELOPMENT OF Lernaa branchialis. F is 

SLIGHTLY, THE OTHER FIGURES GREATLY, ENLARGED. (After 

A. Scott.) 

A, Nauplius, just hatched ; B, young female taken from gills of 
Flounder ; C, free-swimming stage of female, after leaving 
Flounder ; D, free-swimming male ; E, female just after settling 
on gills of Whiting ; F, fully-developed female. 

On the gills of Cod, Haddock, and other common 
fish, we often find a red worm-like parasite, Lern&a 



PARASITES AND MESSMATES 227 

branchialis (Fig. 73, F), which at first sight seems 
to bear no sort of resemblance to a Crustacean. 
The soft body is curiously doubled up, and is 
attached to the host by a narrow neck ; while dissec- 
tion will reveal a small head buried in the flesh of 
the fish's gills, and having three branched outgrowths, 
which penetrate into the surrounding tissues and 
make the attachment of the parasite more secure. 
Near the hinder end of the body are two coiled 
threads, which are the egg-masses. The reduced 
mouth parts and the microscopic vestiges of the 
swimming feet may be detected on and near the 
head, but apart from these it would be hard to 
find any characters to show that the animal is a 
Crustacean. 

The life-history of Lerncza is very remarkable. 
The young are hatched in the nauplius stage 
(Fig. 73, A), and after passing through some further 
free-swimming stages they become parasitic on a 
fish. Curiously enough, however, they choose a 
very different host from that on which the adults 
are found, for at this stage (Fig. 73, B) they attach 
themselves to the gills of one of the Flat-fishes 
(Pleuronectidae), such as the Flounder, Plaice, etc., 
attachment being effected by a frontal cement gland 
similar to that of the larval Caligidae, already 
mentioned. The animal is now without the power 
of swimming, its appendages becoming reduced to 
stumps and losing their setae. After passing some 



228 THE LIFE OF CRUSTACEA 

time in this condition, the larva again acquires the 
power of swimming, and leaves its host. Both sexes 
become mature in this free-swimming stage (Fig. 73, 
C, D), and impregnation is effected. The males 
die without developing further, but the females seek 
a second host, a fish of the family Gadidae, such as 
the Cod, Haddock, etc., and, settling on the gills, 
become metamorphosed (Fig. 73, E) into the adult 
form described above. 

Within the gill cavities of the strange-looking fish 
known as the Angler or Fishing-frog (Lophius 
piscatorius) there may often be found specimens of 
another parasitic Copepod, Chondr acanthus gibbosus. 
It has a soft, unsegmented body about half an inch 
long, provided with numerous blunt lobes which 
give it a very irregular shape. On the under-side, 
near the front, are forked lobes representing two 
pairs of the swimming feet. At the hinder end are 
usually attached a pair of long thread-like egg-masses. 
Just at the point where the egg-masses are attached, 
close inspection of the under-side of the body will 
reveal a very minute maggot-like object. This is 
a male individual, which is attached, like a secondary 
parasite, to the body of the enormously larger female. 

In all the cases mentioned, the animal is parasitic 
in the final state of its existence at least in the 
female sex but there are a few Copepoda which are 
free-swimming, both when young and when adult, 
but parasitic in the intermediate stages. Among the 



ovjr. 



f. 




FIG. 74 STAGES IN THE LIFE-HISTORY OF Hamocera dance, ONE 
OF THE MONSTRILLID^E. (From Lankester's " Treatise on 
Zoology," after Malaquin.) 

A, Free-swimming nauplius larva ; B, embryo after penetrating 
into the body of the worm Salmacina ; C, D, E, successive stages 
in the body of the host ; F, free-swimming adult female. (All 
greatly enlarged, not to same scale.) a', Antennule ; br, brain ; 
c, nauplius eye ; /, swimming feet; g.s., hairs on which the eggs 
are carried ; m, position of mouth ; md, hooked mandible of 
nauplius ; n, nerve cord ; ov, mass of eggs carried by female ; ovy, 
ovary ; pr, absorptive processes. 



230 THE LIFE OF CRUSTACEA 

Copepoda taken by the tow-net in British seas, there 
may sometimes be found species of the family 
Monstrillidae (Fig. 74, F), which are remarkable for 
having no appendages between the antennules and 
the first pair of swimming feet. They have no trace 
of jaws, and only a minute vestige of a mouth-open- 
ing ; while internally there is no food-canal, so that 
the animals are incapable of taking nourishment. 
Their development was for long a mystery, but it 
is now known that the greater part of their life is 
passed as internal parasites in certain bristle-footed 
worms (Polychseta). The young are hatched as 
nauplius larvae (Fig. 74, A) without mouth or food- 
canal, but capable of swimming, and having the 
third pair of appendages (mandibles) furnished with 
strong hooks, by means of which the)' fasten on to 
the worm which is to serve as their host. The 
nauplius bores through the skin of the worm, casting 
its cuticle and losing all its appendages in the 
process, and making its way into one of the blood- 
vessels in the form of a little oval mass of cells 
(Fig. 74, B), within which no organs except the 
degenerating nauplius eye can be detected. It later 
becomes enclosed in a delicate cuticle, and from one 
end two long finger-like processes grow out, which 
are believed to have the function of absorbing 
nourishment from the blood of the host (Fig. 74, C, D). 
Within the cuticle the organs of the adult animal 
are gradually differentiated (Fig. 74, E), and when 



PARASITES AND MESSMATES 231 

fully formed it bores its way through the tissues of 
its host by means of rows of hook-like spines 
surrounding the pointed posterior end of the sac. 
On reaching the surface the enclosing membrane 
bursts, and the adult animal is set free. 

Of all Crustacean parasites, however, perhaps the 
most remarkable in their structure and life-history 
are the Cirripedes of the order Rhizocephala. It is 
not uncommon on the British coasts to find specimens 
of the common Shore Crab or other Crabs which 
carry under the abdomen an oval fleshy body. This 
is the Rhizocephalan Sacculina carcini (Plate XXIX.), 
and it would hardly be possible to guess, from its 
appearance or structure, that it was a Cirripede or a 
Crustacean at all. It is attached to the under-side 
of the Crab's abdomen by a short stalk, and in the 
middle of its opposite surface is a small opening 
which leads into a cavity separating the outer 
" mantle " from the body of the animal. Very often 
this mantle cavity will be found to be full of eggs 
enclosed in sausage-shaped packets. At the point 
where the short stalk enters the abdomen of the 
Crab, it gives off an immense system of fine branching 
roots, which penetrate throughout the body of the 
Crab, and even into its legs and other appendages. 
By means of these roots the Sacculina absorbs 
nourishment from the body-fluids of its host. Like 
most Cirripedes, Sacculina is hermaphrodite, and the 
body within the mantle cavity contains only the 



232 



THE LIFE OF CRUSTACEA 



reproductive organs of the two sexes and a small 
nerve ganglion representing the whole of the nervous 
system. There is no mouth, no food-canal, and no 
trace of appendages. Another Rhizocephalan, Pelto- 
gaster, is not uncommonly found attached to the 





FIG. 75 FREE-SWIMMING STAGES OF Sacculina carcini. MUCH 
ENLARGED. (After Delage ) 

A, Nauplius ; B. cypris stage. 

abdomen of Hermit Crabs. Although the nauplius 
larva of Sacculina was described, and its resemblance 
to that of the Cirripedia pointed out, as long ago as 
1836, by that acute observer, J. Vaughan Thompson, 
it is only recently that the full life-history has been 
made known by the researches of Professor Delage 



PARASITES AND MESSMATES 233 

and Mr. Geoffrey Smith. The nauplius larva 
(Fig. 75, A) resembles that of the normal Cirripedes, 
especially in the shape of the dorsal shield, which 
is drawn out on either side in front into a pair of 
fronto-lateral horns. It has, however, no mouth, 
and the food-canal is quite absent. As in the normal 
Cirripedes, the nauplius is followed by a cypris stage 
(Fig. 75, B), also mouthless, and it is in this form 
that the Sacculina seeks the Crab on which it is to 
become parasitic. It would be almost impossible for 
the cypris larva to settle on that part of the Crab 
where the adult Sacculina is afterwards to appear, 
since the Crab usually has its abdomen closely 
pressed against the under-side of its thorax. The 
larva therefore attaches itself on some exposed part 
of the Crab, often on one of the legs, clinging to a 
hair by means of its antennules. It bores through 
the cuticle at the base of the hair, and the contents 
of its body pass into the interior of the Crab as a 
little mass of cells, the empty cypris shell being cast 
off. This mass of cells, which constitutes the embryo 
Sacculina, is carried about by the blood-currents of 
the Crab till it reaches the under-side of the intestine, 
where it becomes attached. It now begins to send 
out roots (Fig. 76), and as it grows the central mass 
travels backwards along the intestine of the Crab till 
it reaches the place where the adult parasite is to 
emerge. As the mass increases in size, and the 
organs of the Sacculina become differentiated within 



234 THE LIFE OF CRUSTACEA 

it, its presence causes the living tissues between it 
and the external cuticle to degenerate, so that when 
the Crab moults an opening is left through which 
the body of the parasite protrudes. Owing, no doubt, 
to the drain on its system due to the presence of the 
Sacculina, the Crab ceases to grow, and it does not 
moult again as long as the parasite remains alive. 




r 



FIG. 76 EARLY STAGE OF Sacculina WITHIN THE BODY OF A CRAB. 
(After G. Smith.) 

i, Intestine of the Crab ; s, body of the Sacculina, which afterwards 
emerges on the under-surface of the Crab's abdomen ; r, roots of 
the Sacculina. 

In addition to this arrest of growth, Sacculina 
produces in its hosts other changes, which affect 
chiefly the reproductive organs and the structures 
associated therewith. Crabs of either sex infected 
with Sacculina are incapable of breeding ; the genital 
gland (ovary or testis) is found on dissection to be 
shrivelled up, and the external characters indicative 
of sex become strangely modified. The changes have 



PARASITES AND MESSMATES 235 

been most fully studied in the case of a kind of 
Spider Crab common at Naples Inachus mauritanicus 
In this species it is found that females infected with 
Sacculina show no conspicuous external modification, 
except that the abdominal appendages, which in the 
normal females serve for the attachment of the eggs, 
are greatly reduced in size. Infected males, how- 
ever, may assume to a greater or less degree the 
characters proper to the female sex. Some males 
show little change, except that the chelipeds remain 
small and flattened, as in the females and non- 
breeding males. Other specimens have, in addition, 
the abdomen much broader than in normal males, 
and sometimes as broad as in the females. Finally, 
some males develop on the abdomen, in addition to 
the rod-like appendages on the first and second 
somites, characteristic of the male sex, two-branched 
appendages on the next three somites, as in the 
females ; these individuals are, in fact, so completely 
intermediate in character between the two sexes that 
it is only by dissection that it is possible to recognize 
them as modified males. 

An indication of the way in which the degenerate 
Rhizocephala have been derived from normal Cir- 
ripedes is given by a peculiar species of pedunculate 
Barnacle, Anelasma squalicola, which lives attached to 
Sharks and Dogfish in the North Sea. In Anelasma 
the peduncle becomes deeply buried in the flesh 
of the Shark, and its surface is covered with short 



236 THE LIFE OF CRUSTACEA 

branching, root-like filaments. As in the case of 
the Rhizocephala, these roots appear to absorb 
nutriment from the host, and, although Anelasma 
possesses a food-canal and mouth, the cirri are 
reduced in size and devoid of hairs, so that they 
cannot be used for obtaining food as in ordinary 
Barnacles. 



CHAPTER XI 

CRUSTACEA IN RELATION TO MAN 

THE Crustacea come into relation with human 
life in the most obvious and direct way in the 
case of those species that are used for food. The 
number of species so used in various parts of the 
world is very large, almost the only necessary condi- 
tion being that the species shall be sufficiently large 
and abundant to make it worth while to fish for it. 

As most of the larger Crustacea belong to the 
Decapoda, it is this order that supplies practically all 
the edible species, almost the only exceptions being 
a few Barnacles which are eaten in various parts 
of the world. Thus the sessile Barnacle Balanus 
psittacus, found on the coasts of Chili, and growing 
to a length of 9 inches by 2 or 3 inches diameter, is, 
according to statements quoted by Darwin, " univer- 
sally esteemed as a delicious article of food," and the 
pedunculate Pollicipes cornucopia is used for food on 
the coasts of Brittany and Spain. 

By far the most valuable of all the edible Crustacea 
are the European and American Lobsters (Homarus 

23? 



238 THE LIFE OF CRUSTACEA 

gammarus and H. americanus) . The former is found 
on the coasts of Europe from Norway to the 
Mediterranean, living mostly a short distance below 
low- water mark wherever the bottom is rocky. At 
some places, as for instance at Worthing, Lobsters 
are common on a sandy bottom, but as a rule they 
seem to prefer localities where the crevices of a rough 
hard bottom afford abundance of shelter. They are 
usually caught in traps known as " Lobster pots " or 
"creels," which vary in construction in different 
localities. In some cases they are made of wicker- 
work, hemispherical in shape, with a funnel-shaped 
opening on top, so devised as to permit the Lobsters 
to enter easily, while preventing their escape. 
Another form is semi-cylindrical, with a framework of 
wood covered with netting or with wooden spars, and 
having two funnel-shaped entrances at the sides. 
These traps are baited with pieces of fish, preferably 
stale, and are sunk in suitable places, each attached 
by a line to a buoy or float. 

Important Lobster fisheries are carried on in 
Norway, Scotland, England, Ireland, Heligoland, and 
other parts of the coasts of Northern Europe. In the 
South the Lobster fishery is of less importance, other 
large Crustacea, especially the Spiny Lobster, being 
more abundant and more highly esteemed. 

The American Lobster, as already mentioned, 
closely resembles the European species, the chief 
difference being in the form of the rostrum (see 



CRUSTACEA IN RELATION TO MAN 239 

Fig. 9, p. 32). It is found on the Atlantic coast 
from Labrador to Cape Hatteras, but it is not 
abundant south of New Jersey. The canning of 
Lobsters is a very important industry in Newfound- 
land, the Maritime Provinces of Canada, and the 
Northern New England States. 

The only other species of the genus Homarus (H. 
capensis) is found at the Cape of Good Hope, but it is 
of small size and is of no economic importance. 

The European Lobster rarely reaches a weight 
of 10 pounds, although individuals of 14 pounds 
weight have been caught. In America, there are 
authentic records of Lobsters weighing 20 and even 
23 pounds. 

The bad effects of over-fishing have become 
apparent of late years, especially on the American 
coast, in the reduced average size of the Lobsters 
caught rather than in a diminution of the total yield 
of the fishery. Numerous experiments in legislation 
have been made with a view to checking the deple- 
tion of the fishing-grounds, but in no case with con- 
spicuous success. A "close time " for the spawning 
Lobsters has often been tried, but the fact that the 
female carries the eggs attached to her body for 
nearly a year after spawning makes it quite impos- 
sible to give effective protection by this means. In 
most Lobster-fishing districts a minimum size is 
fixed by law, below which it is illegal to take or sell 
Lobsters, and in many cases also the capture of 



240 THE LIFE OF CRUSTACEA 

females carrying spawn, or, as it is termed, "in 
berry," is prohibited. 

The so - called " Norway Lobster " (Nephrops 
norvegicus Plate XXX.), the " Dublin Prawn " of the 
London fishmongers, is a smaller and much less 
valuable species than the common Lobster. It may 
be recognized at once by its long and slender claws, 
furnished with rows of tubercles or blunt spines, and 
by the sculptured markings on the somites of the 
abdomen. When alive it is of an orange colour, 
beautifully marked with red and white. It differs 
considerably in its habits from the common Lobster, 
living at a considerably greater depth (30 to 60 
fathoms in Norway), and on a muddy bottom. It is 
generally taken by trawling, and is captured in large 
quantities by trawlers fishing in various parts of the 
North Sea. Since it must be cooked soon after it is 
caught, and cannot easily be brought to market alive 
like the common Lobster, only a small number of 
those actually caught are made use of. Formerly most 
of those sold in London were caught in the Irish 
Sea (whence the name of " Dublin Prawn "), but the 
North Sea is now the chief source of supply. The 
species is found in suitable localities from Norway 
to the Mediterranean, and is especially abundant in 
the Adriatic, where it is caught and sold in Venice 
and elsewhere under the name of " Scampo." 

The Spiny Lobster, Rock Lobster, or Sea-craw- 
fish (Palinurus vulgaris Plate V.), is common on the 



PL A TE XXX 




THE "NORWAY LOBSTER," Nephrops norveg-icus, ABOUT 

ONE-THIRD NATURAL SIZE 
C From Brit. Mus. Guide) 



CRUSTACEA IN RELATION TO MAN 241 

south and south-west coasts of the British Islands, 
becoming rare in the north, although specimens 
have been found as far north as Orkney, and there is 
a single record of the species from the West of 
Norway. It is far less commonly used for the table 
in this country than in France, where it is known as 
" Langouste " and is very highly esteemed. 

Various species of Spiny Lobsters belonging to 
the same family (Palinuridse) as the European 
species are found in different parts of the world. In 
tropical countries the species of Panulirus are com- 
monly used for food (for example, P. interruptus in 
California and P. fasciatus in India), as are species of 
Jasus in South Africa, Australia, and New Zealand. 
Recently a consignment of Spiny Lobsters (Jasus 
lalandii) was sent to the London market from the 
Cape, but it appears that the experiment was not 
altogether successful. 

Belonging to the same tribe (Nephropsidea) as 
the Lobsters are the fresh-water Crayfishes. The 
English Crayfish (Astacus pallipes) is common in 
many rivers as far north as Lancashire, and in some 
parts of Ireland, but is not found in Scotland. It is 
not much esteemed for the table, and although small 
numbers are sent to Billingsgate, chiefly from 
Leicestershire, they are said to be used only for 
garnishing dishes. The same species occurs on the 
Continent of Europe, chiefly in the west and south 
(France, Germany, Switzerland, Spain, Italy, and 
16 






242 THE LIFE OF CRUSTACEA 

the Balkan Peninsula). It is known in France as 
" Ecrevisse a pattes blanches " (from the whitish 
colour of the under-side of the large claws), and in 
Germany as " Steinkrebs," and is distinguished, 
among other characters, by the shape of the rostrum 
(Fig. 77, B), which has a tooth on each side close to 
the point. Far more important as an article of food 
is the larger Astacus fluviatilis, the " Ecrevisse a 
pattes rouges " or " Edelkrebs," which is found in 



B. 








FIG. 77 ROSTRUM AND FORE PART OF CARAPACE, SEEN FROM 
ABOVE, OF (A) RED-CLAWED CRAYFISH (Astacus fluviatilis) AND 
(B) WHITE-CLAWED OR ENGLISH CRAYFISH (Astacus pallipes) 

France, Germany, Austria, Southern Sweden, Russia, 
etc. In this species the under-side of the large claws 
is generally of a fine red colour, and the rostrum 
(Fig. 77, A) has a pair of side-teeth about the middle 
of its length, and a long slender point. The red- 
clawed Crayfish is an important article of commerce 
on the Continent, and is sent to the London market 
in considerable numbers, chiefly from Germany and 
South- West Russia. In France it is cultivated for 
the market in " Crayfish farms " on a large scale. 
A species of Crayfish (A . leptodactylus} occurring in 



CRUSTACEA IN RELATION TO MAN 243 

the Lower Danube and in other rivers flowing into 
the Black Sea sometimes finds its way to the London 
market, although it is less valued than the red- 
clawed species. It is distinguished by its long and 
slender claws, by the spiny edges of the rostrum, and 
by other characters. A fourth species (A . torrentium), 
occurring chiefly in Central Europe, is very closely 
allied to A.pallipes, and, like it, is of little value for 
the table. 

Within the last thirty years the Crayfish fisheries 
of Western Europe have suffered heavily from out- 
breaks of an epidemic disease which has all but 
exterminated these animals in certain districts. 
In this country it is said to be responsible for the 
almost complete disappearance of Crayfish from 
localities where they were formerly plentiful, as, for 
instance, in the neighbourhood of Oxford. The 
cause of the disease is believed to be a protozoan 
parasite belonging to the group Myxosporidia. 

In other parts of the world it does not seem that 
the fresh-water Crayfishes are of much importance 
as an article of food. Some species of Cambarus are 
so used to a limited extent in the United States, and 
the gigantic Astacopsis serratus (Plate XX.) is known 
as the " Murray River Lobster " in the markets 
of Sydney and Melbourne. 

The Decapods of the suborder Natantia comprise 
a large number of edible species, generally known 
as Shrimps and Prawns. The Common Shrimp, 






244 



THE LIFE OF CRUSTACEA 



Crangon vulgaris (Fig. 78), which is plentiful on the 
British coasts wherever the bottom is sandy, is about 
two or three inches long, and when alive is of a 
translucent greyish colour speckled with brown. It 
differs from most of the Natantia in having the body 
somewhat flattened from above downwards, and the 




FIG. 78 THE COMMON SHRIMP (Crangon vulgaris). NATURAL SIZE 

rostrum very short. When boiled, it is of a reddish- 
brown colour, and from this it is sometimes known 
as the " Brown Shrimp." On many parts of the 
coast the Shrimp fishery is of considerable im- 
portance. Most often the Shrimps are caught by 
means of a large bag-net attached to a semicircular 
hoop with a long handle, and pushed over the surface 



CRUSTACEA IN RELATION TO MAN 245 

of the sand by a fisherman wading in the water at 
ebb-tide. 

A variety of species are sold in England under the 
name of Prawns. The largest of the native species, 
to which the name of Common Prawn is perhaps 
most properly restricted, is Leander serratus. It 
grows to a length of over 4 inches, and has a long 
serrated rostrum extending beyond the antennal 
scales and curving upwards at the point. The first 
and second pairs of legs end in small pincer-claws. 
When alive the animal is very transparent, and 
beautifully marked with bands of brown and red on 
the body and limbs. A smaller species of the same 
genus (L. squilla), distinguished by the much shorter 
and straighter rostrum, and another very similar 
species of which the proper name appears to be 
L. adspersus (often known as L. fabricii), are said to 
be sold on some parts of the English coast as " Cup 
Shrimps." 

Much commoner, at least in the London market, 
than the species of Leander is Pandalus montagui, 
often sold under the general name of Prawn, but 
sometimes called the " Pink Shrimp." This re- 
sembles Leander serratus in having a long, serrated, 
up-curved rostrum, but differs from it strikingly in 
the form of the anterior pairs of feet. The first pair 
appear to the naked eye to have no pincer-claws, but 
to end in a sharp point, resembling the third maxilli- 
peds, which are just in front of them. As a matter of 



246 



THE LIFE OF CRUSTACEA 



fact, they do have pincers, but so minute that they 
can only be detected by microscopic examination. 
The feet of the second pair are unequal in length on 
the two sides, that on the left side being the longer, 
and are very slender. They end in small pincers, 
and examination with a pocket-lens will show that 
the carpus, or "wrist," and the segment below it 
(merus) are broken up into a large number of short 




FIG. 79 THE NORWEGIAN DEEP-WATER PRAWN (Pandalus borealis), 
FEMALE. (After Sars.) 

The second leg of the right side is indicated by dotted lines. 

segments, so that the limb is extremely flexible. 
When alive, the animal is even more handsomely 
marked than the Common Prawn. 

A large species of Prawn is now imported to this 
country in considerable quantities from Norway. 
This is Pandalus borealis (Fig. 79), a species closely 
allied to the last-named, but differing in the longer 
and more slender rostrum and in many other 
characters, as well as in its larger size (specimens 



CRUSTACEA IN RELATION TO MAN 247 

have been recorded of 6 inches in total length). It 
also differs in its habitat, for while P. montagui lives 
in shallow water, or even between tide- marks, 
P. borealis occurs at depths of 30 to 60 fathoms in the 
Norwegian fjords. The recent development of the 
fishery for P. borealis in Norway is a striking example 
of the practical value of zoological research. Until 
1898 the species was hardly known except to zool- 
ogists, although a small fishery was carried on in 
the Drammen Fjord, near Christiania. The investiga- 
tions of the naturalists employed by the Norwegian 
Department of Fisheries showed that the species 
existed in vast numbers in the deeper water of many 
of the fjords, and that it could be captured in abun- 
dance by means of a suitably-devised trawl-net. As 
a result, a very profitable fishery was established, and 
the " deep-water Prawns " are now not only largely 
consumed in Norway, but are exported in increasing 
quantities to the English and other markets. 

In the warmer seas the large Prawns of the genus 
Penceus are of considerable importance. Thus, in the 
Mediterranean countries, Penceus caramote (Plate IV.) 
is highly esteemed for food, and P. setifer and 
P. brasiliensis are largely consumed in the Southern 
United States. P. monodon and other species are 
eaten in India. An attempt has been made to send 
a species of the same genus (apparently P. indicus) in 
a frozen state from Queensland to the London 
market. 



248 THE LIFE OF CRUSTACEA 

Numerous other species of Natantia are used for 
food in various parts of the world, but the only ones 
that need be further mentioned here are the River 
Prawns of the genus Palczmon, which are abundant 
in the fresh waters of most tropical countries, and 
sometimes grow to a very large size. They are 
generally distinguished by the fact that the legs of 
the second pair are very long, forming powerful 
pincer-claws. In the West Indies and Central 
America, P. jamaicensis (Plate XXL), which reaches 
a length of 10 inches exclusive of the great claws, is 
sold in the markets, while in India and elsewhere 
in the East P. carcinus, which grows to an even 
greater size, and other smaller species, are used for 
food. The fresh-water Prawns of the family Atyidae, 
on account of their small size, are not of much 
importance from this point of view, but Professor 
Hickson states that the little Caridina nilotica, a very 
widely-distributed species, is eaten in Celebes. 

Among British Crustacea, the next in importance 
to the Lobster as an article of food is the Edible 
Crab, Cancer pagurus (Plate XXX I.) , known in 
Scotland as the " Partan." Like the Lobster, it is 
found on rocky coasts in shallow water, and young 
specimens are often taken between tide-marks. It 
grows to a size of more than 10 inches across the 
shell, and may reach a weight of 12 pounds. The 
means used for its capture are the same as in the 
case of the Lobster, and the fishery is of considerable 






PLATE XXXI 




CRUSTACEA IN RELATION TO MAN 249 

importance on many parts of the British coasts. 
On the other hand, a Connemara fisherman, who 
was using these Crabs for bait, received with incre- 
dulity the statement that they were good for human 
food! 

The Shore Crab, Carcinus m&nas (Plate IX.), is 
not of much importance as food in this country, 
although it is recorded that fifty years ago great 
numbers were brought to the London market. On 
the shores of the Mediterranean and Adriatic, how- 
ever, and especially in Venice, this species is re- 
garded as a delicacy, particularly in the soft-shelled 
state after moulting. 

On the Atlantic coast of North America, the 
most important edible Crustacean after the Lobster 
is the " Blue Crab " (Callinectes sapidus}, one of the 
Swimming Crabs (Portunidae). This is consumed 
in large quantities, especially in the soft-shelled state. 
Several other species of Crabs are eaten in America, 
including the little " Oyster Crab," a species ot 
Pinnotheres living in the American Oyster. From 
its small size, and the difficulty of obtaining it in 
numbers, it is a very costly delicacy. 

In the East Indies the most important edible 
Crabs are various species of Portunidae, especially 
the large Scylla serrata and Neptunus pelagicus. 

Except as food, the Crustacea are of very little 
direct use to man. Almost the only instance in 
which they are otherwise utilized is in the case of 



250 THE LIFE OF CRUSTACEA 

a 'species of sessile Barnacle (Balanus) which is 
cultivated in Japan for use as manure. The method 
of culture has been described by Professor Mitsukuri. 
Bunches of bamboo "collectors," like those used 
for the collection of oyster-spat, are fixed into the 
ground on tidal flats. After two or three months 
they are taken up, and the Barnacles with which 
they have become covered are beaten off and sold 
for use as manure. 

Apart from their direct utility, however, the Crus- 
tacea are indirectly of great importance as providing 
a large part of the food-supply of marketable fishes. 
From this point of view, a study of the habits and 
distribution of the commoner species may be of 
practical value in throwing light on the migrations 
and other obscure points in the life-history of the 
fishes that prey upon them. As an example of this, 
we may refer to some investigations on the Mackerel 
fishery recently carried out by the naturalists of 
the Marine Biological Association at Plymouth. In 
the spring and early summer months the Mackerel 
migrate into inshore waters for the purpose of 
spawning. During this period the fish congregate 
in shoals at the surface of the sea, and are captured 
in drift-nets. The extent of this " shoaling " varies 
greatly from year to year, and determines whether 
the season shall be a profitable one for the fishermen 
or not. When shoaling, the fish feed exclusively on 
plankton, consisting largely of Copepoda, and it has 



CRUSTACEA IN RELATION TO MAN 251 

been shown by Mr. G. E. Bullen that the fluctuations 
in the yield of the Mackerel fishery from year to year 
follow very closely the fluctuations in the abundance 
of the Copepod plankton on the fishing-grounds. 
The investigation has been carried a step farther by 
Dr. E. J. Allen, who points out that the abundance 
of Copepods is determined by the abundance of the 
Diatoms and other minute vegetable organisms of 
the plankton. These organisms are very largely 
influenced by the amount of sunshine during the 
period of their development in the earlier months of 
the year. Dr. Allen gives a diagram showing for 
each of seven years (1902-1908) the average number 
of hours of bright sunshine during the months of 
February and March in the South- West of England. 
With this he compares the number of fish caught 
in the month of May in each of these years by 
certain vessels engaged in the western Mackerel 
fishery. The correspondence between the two is 
very striking indeed, and justifies his conclusion 
that the amount of sunshine in the early months of 
the year determines the abundance of the vegetable 
life of the plankton, and through it of the Copepods 
and other animals which form the bulk of the 
plankton a little later in the year ; and although 
there are doubtless other influences at work deter- 
mining the success or failure of the fishery, it is 
largely a matter of the richness or poverty of the 
plankton harvest. 



252 THE LIFE OF CRUSTACEA 

None of the Crustacea can be regarded as directly 
harmful to man. They have not the power of 
inflicting envenomed wounds which renders some 
other Arthropods, such as Scorpions, some Spiders, 
Centipedes, and Insects, formidable in spite of their 
small size ; and although blood-curdling tales of the 
ferocity of the Land Crabs are to be found in the 
accounts of old voyages, even the largest of these is 
hardly an antagonist to be dreaded. 

A considerable number of invertebrate animals, 
not of themselves noxious, are now known to be 
the indirect cause of much serious injury to human 
life by harbouring and disseminating organisms 
which produce disease. The progress of research is 
adding, almost every day, to the number of species 
known to be disease-carriers, and it is possible that 
in the future some Crustacea as yet unsuspected 
may be added to the list. 

At present, however, there is only one case in 
which a Crustacean has been shown to be concerned 
in the transmission of a parasite of man. The 
" Guinea-worm," Filaria (or Dracunculus) medinensis, 
is a parasite belonging to the group of " Thread- 
worms " (Nematoda) which causes dangerous ab- 
scesses under the skin of the legs in many parts 
of tropical Africa. It has been shown that the 
embryos of the worm, which are discharged in vast 
numbers on the bursting of the abscess, do not 
develop unless they fall into water containing certain 



CRUSTACEA IN RELATION TO MAN 253 

species of the Copepod Cyclops (see Fig. 14, p. 39). 
In some way not yet understood, the embryos 
penetrate into the body cavity of the Cyclops, where 
they undergo a metamorphosis. For their further 
development it is necessary that the Cyclops should 
be swallowed by man, as may easily happen in 
drinking water from a pond. When the Cyclops is 
digested the larval worms are set free, and they bore 
their way through the tissues of their human host 
till they reach the place (generally under the skin of 
the leg) where they complete their development and 
produce the innumerable embryos that are set free 
in the way just described. 

A few Crustacea inflict a certain amount of injury 
on man in more indirect ways. In tropical countries, 
Land Crabs are often troublesome in gardens, and 
may cause serious damage to young plants in sugar- 
cane plantations and rice-fields. In gardens in this 
country, the Woodlice, as already mentioned, are 
sometimes destructive to seedlings and delicate 
plants. The little fresh-water Isopod, Asellus aquati- 
cus, is accused of destroying the nets used in fishing 
for Pollan in Lough Neagh in Ireland. 

Probably the most important of all Crustacea, 
however, as regards their destructive activity, are the 
species which bore into wood, and sometimes do exten- 
sive damage to the submerged timber of piers, jetties, 
and similar structures. On our own coast the most 
destructive is a little Isopod known as the " Gribble " 







254 THE LIFE OF CRUSTACEA 

(Limnoria lignorum Fig. 80), which is distributed 
from Norway to the Black Sea,[and^occurs also on 
the Atlantic coast of North America. Several species 
of the same genus having similar habits are found in 
other parts of the world. The Gribble was first 
discovered as a British species by Robert Stevenson, 
the celebrated lighthouse engineer, who found it in 




FIG. 80 THE GRIBBLE (Limnoria lignorum). MUCH ENLARGED 
(From British Museum Guide, after Sars.) 

1811 destroying the woodwork employed in the 
erection of the Bell Rock Lighthouse, and sent 
specimens to Dr. Leach of the British Museum. 
The animal is only about one-eighth of an inch in 
length, and its cylindrical burrow is about one- 
fifteenth of an inch in diameter, and penetrates for a 
depth of one or two inches. The excavation of the 
wood is effected by means of the mandibles, which 
are unusually strong; and when the animals are 



PLATE XXXII 




PIECE OF TIMBER FROM RYDE PIER SHOWING DAMAGE CAUSED BY 

Limnoria AND Chelura 
(From Brit. Mus. Guide) 



CRUSTACEA IN RELATION TO MAN 255 

numerous the burrows are driven so close together 
that the surface of the wood is reduced to a spongy 
mass which is rapidly washed away by the waves 
(Plate XXXII.). The Gribble is often accompanied 
by another Crustacean of similar habits, the Amphi- 
pod Chelura terebrans. The latter is about one-fifth 
of an inch in length, and differs from most Amphi- 
pods in having the body somewhat flattened from 
above downwards instead of from side to side. The 
burrows made by Chelura are shallower than those of 
the Gribble, and generally run more or less parallel 
to the surface of the wood. 



* 

* 

f ' f 

\ 





* 

' 






CHAPTER XII 
CRUSTACEA OF THE PAST 

SINCE the acceptance by naturalists of the theory 
of Evolution as indicating the mode of origin 
of the various forms of life now existing, one of 
the chief lines of biological investigation has had 
for its object the reconstruction of the pedigree (or, 
as it is called, the " phylogeny ") of the larger groups 
of the animal and vegetable kingdoms. In attempt- 
ing to do this, there are three main sources from 
which evidence may be drawn. The results of Com- 
parative Anatomy enable us to decide with more or 
less confidence as to the degrees of relationship 
between the groups of organisms, and to distinguish 
between the more primitive and the more specialized ; 
the study of Embryology is, at least, an indispensable 
adjunct to Comparative Anatomy, even if it does not, 
as was once supposed, give us an actual recapitula- 
tion of ancestral history ; and, finally, the study of 
Fossil Remains holds out the hope that we may be 
able to find the ancestral types themselves. 

It is clear that evidence from the last-named 
256 



CRUSTACEA OF THE PAST 257 

source, when it is available, is the most important of 
all, since the order of succession of the various types 
is given by that of the rock strata in which they 
occur, and we can be quite certain that we are 
dealing, if not with the actual ancestors, at least 
with the forerunners of existing species. The " im- 
perfection of the geological record," however, is so 
great that the organisms preserved in the fossil state 
represent only an insignificant part of the whole 
number of organisms that have lived on the globe 
since life began ; and it is not surprising, therefore, 
that in many groups the study of fossils has 
hitherto afforded little help towards the working out 
of their genealogical history. Thus, among Crus- 
tacea there are many important groups such as the 
Copepoda, which are entirely unknown as fossils, 
their small and delicate bodies being ill adapted for 
preservation, although there is every reason to 
suppose that they are a very primitive and very 
ancient group. In many fossil Crustacea only the 
hard shell or carapace has been preserved, the 
appendages being lost or represented only by in- 
decipherable fragments, and in some cases it is 
hardly possible to guess at the affinities of the 
animals. Further, several important groups are 
already represented in some of the oldest of the 
fossil-bearing rocks at present known, and the 
differentiation of these groups must have taken place 
in the dark ages before the record of the fossils 



258 



THE LIFE OF CRUSTACEA 



begins. In spite of these disadvantages, however, 
the study of fossil Crustacea does throw considerable 
light on the evolution of the group, and it is likely 
that interesting results in this direction await future 
investigations. 

In the earliest fossiliferous rocks the most abundant 
and important Arthropods are the Trilobites (Fig. 81), 





FIG. 81 RESTORATION OF A TRILOBITE (Triarthrus becki), SHOWING 
THE APPENDAGES. UPPER SIDE ON RIGHT, UNDER-SIDE ON 
LEFT. SLIGHTLY ENLARGED. (After Beecher.) 

an extinct group which appears to have been related 
to the primitive Crustacea. The name Trilobite 
refers to the three-lobed form of the body when seen 
from the dorsal side, most species having a pair of 
grooves running lengthwise which divide off a middle 
lobe containing the principal organs of the body from 
two lateral " pleural " expansions covering the limbs. 



CRUSTACEA OF THE PAST 259 

The head-shield shows indications of being com- 
posed of five segments, and bears a pair of sessile 
compound eyes. It is followed by a number (up 
to twenty-six) of free somites, and the body ends in a 
tail-shield, or "pygidium," which is often plainly com- 
posed of several somites fused together. Although 
Trilobites are among the commonest and most 
familiar of fossils in the older rocks, the nature of 
their appendages remained quite unknown until 
within recent years, when specimens of several 
species showing the structure of the limbs and 
under-side of the body were discovered in America. 
From these it appears that the head bore in front 
a pair of long thread-like antennae and four pairs 
of two-branched appendages, each with a jaw pro- 
cess, or "gnathobase," turned towards the mouth, 
which is covered below by a large anterior lip, or 
" hypostome." It seems probable that the five pairs 
of head-appendages correspond respectively to the 
antennules, antennas, mandibles, maxillulae, and 
maxillae, of Crustacea ; but the second pair appear 
to have acted as jaws, retaining the gnathobase which, 
among Crustacea, is only hinted at by the hooked 
spine on the antenna of the nauplius larva. 

Each of the free somites and of those forming the 
tail-shield bears a pair of two-branched appendages, 
not differing greatly from the posterior appendages 
of the head, but becoming smaller and more flattened 
towards the hinder end of the body. The numerous 



260 THE LIFE OF CRUSTACEA 

genera and species of Trilobites present great differ- 
ences in the form and ornamentation of the dorsal 
surface of the body, and it is probable that con- 
siderable differences may also have existed in the 
structure of the limbs, which are only known in two 
or three species. Some Trilobites are among the 
most ancient of known fossils, being found in rocks 
of the Lower Cambrian epoch. The group reaches 
its maximum development in the Ordovician, and 
the number of the species and size of the individuals 
gradually diminish through the Silurian and Devonian 
till they become extinct at the close of the Carbon- 
iferous epoch, except for a single species found in 
rocks of Permian age in America. 

Although zoologists are not all agreed as to the 
precise systematic place to be assigned to the Trilo- 
bites, there can be little doubt that they were related 
more or less closely to the most primitive Crustacea, 
and they are of special interest as preserving for us 
the stage in which the second pair of appendages 
were still used as biting jaws, and had not moved 
forwards in front of the mouth to become antennae, 
as in all living Crustacea. 

Contemporary with some of the earliest Trilobites, 
however, are undoubted Crustacea, which, so far as 
we know their structure, are not very different from 
types now living. In the Cambrian epoch the 
Branchiopoda appear to be represented by Protocaris, 
which in its general form resembles Apus ; and 



CRUSTACEA OF THE PAST 261 

there are a variety of genera and species of Ostra- 
coda, although, since their shells alone are preserved, 
it is not possible to determine their exact relations 
to existing forms. In the succeeding Ordovician 
and Silurian epochs we first meet with the remains 
of Barnacles, and it is interesting to note that some 
of them are referred to the genera Pollicipes and 
Scalpellum, which are represented by numerous 
species in the seas of the present day. Along with 
these, however, are some strange-looking forms 
(Turrilepas, etc.), having the body covered with rows 
of overlapping plates. If these are really Cirripedes, 
they must have differed considerably in structure 
from the more modern types. 

The Malacostraca are more interesting from the 
point of view of palseontology than the other sub- 
classes of Crustacea, since the evolution of the group 
appears to have taken place within the period covered 
by the fossil records, and it is possible to trace the 
course of that evolution at least, in its broad out- 
lines. It has already been pointed out that the most 
primitive of existing Malacostraca are the Phyllo- 
carida (Nebalia and its allies), which are in several 
respects intermediate between the higher Malacos- 
traca and the Branchiopoda ; and it is interesting to 
find that fossils apparently belonging to the Phyl- 
locarida are found far earlier than any of the other 
Malacostraca. In the Cambrian, and more abund- 
antly in the Ordovician and Silurian, there are found 



262 THE LIFE OF CRUSTACEA 

Crustacea (Fig. 82) that resemble Nebalia in having 
a large bivalved carapace, with a movable beak-like 
plate in front, a projecting abdomen without con- 
spicuous limbs, and a pair of large spines at the 
sides of the telson. Unfortunately, we have almost 
no knowledge of the structure of the limbs ; but it 
can hardly be doubted that these very ancient 
Crustacea were allied to the existing Phyllocarida, 




FIG. 82 Ceratiocaris papilio, ONE OF THE FOSSIL PHYLLOCARIDA. 
(From Lankester's " Treatise on Zoology," after H. Woodward.) 

a. Traces of antennules ; m, possibly mandibles ; r, rostral plate 

and that they included the forerunners of the higher 
Malacostraca. 

It is in the Carboniferous epoch, in all probability, 
that we must look for the origin of most of the 
existing orders of Malacostraca. In the rocks of 
this age in different parts of the world there have 
been found a number of undoubted Malacostraca, 
nearly all of the shrimp-like form which there is 
good reason to believe to be a primitive character- 



CRUSTACEA OF THE PAST 263 

istic. Some of these (Pygocephalus Fig. 83) have 
recently beea shown to possess a brood-pouch formed 
of overlapping plates on the under-side of the thorax, 
and thus resemble the existing Mysidacea, which 
stand at the base of the Peracaridan series of orders. 
Others have a pair of strong side spines near the tip 
of the telson, and in other ways resemble the recent 




FIG. 83 Pygocephalus cooperi, FROM THE COAL-MEASURES : UNDER- 
SIDE OF A FEMALE SPECIMEN, SHOWING THE OVERLAPPING 
PLATES OF THE BROOD-POUCH. (From Lankester's " Treatise on 
Zoology," after H. Woodward.) 



Euphausiacea, so that they may have been primitive 
members of the Eucaridan series. 

Among the Crustacea of the Carboniferous and 
Permian epochs, there are a number of forms of 
which the affinities were until recently quite 
obscure. They have two -branched antennules, a 
scale-like exopodite on the antenna, and the last 
pair of appendages (uropods) form, with the telson, 



264 THE LIFE OF CRUSTACEA 

a tail-fan. In these points they resemble the shrimp- 
like forms, but there is no carapace, and all the 
somites of the thorax are distinct, so that the form 
of the body is rather that of an Amphipod or Isopod. 
On the discovery of the remarkable Crustacean 
Anaspides (Fig. 84), which lives in fresh- water pools 
in the mountains of Tasmania, it was pointed out 
that it agreed with the fossil genera Uronectes, Pal<zo- 




FIG. 84 THE TASMANIAN "MOUNTAIN SHRIMP" (Anaspides 
tasmania), A LIVING REPRESENTATIVE OF THE SYNCARIDA. 
SLIGHTLY ENLARGED 

c.gr. t "Cervical groove," marking off the first thoracic somite; 
ii-viii, the remaining thoracic somites; 1-6, the abdominal 
somites 

can's, and their allies, in those very characters in 
which they differed from all other Crustacea, and that 
it must be regarded as a surviving representative of 
the ancient group to which the name of Syncarida 
had been given. The more recent discoveries of 
living forms, Paranaspides from the Great Lake of 
Tasmania and Koonunga from fresh- water pools near 



CRUSTACEA OF THE PAST 



265 



Melbourne, and of the fossil Pr&anaspides (Fig. 85) 
from the Coal-measures of Derbyshire, have tended 
to support this conclusion. There can be little 
doubt that the Syncarida arose during the Carbon- 
iferous epoch (or earlier) from primitive shrimp-like 
forms which lost the carapace ; but, after flourishing 
for a relatively brief period, the'group dwindled away, 




FIG. 85 Praanaspides precursor, ONE OF THE FOSSIL SYNCARIDA, 

FROM THE COAL - MEASURES OF DERBYSHIRE. SLIGHTLY EN- 
LARGED. (After H. Woodward.) 

although a few survivors have lingered on, like so 
many other " living fossils," in the isolated Australian 
region. 

It must be pointed out that, in spite of the re- 
semblance of the body of Anaspides to that of an 
Amphipod, the Syncarida can have had no close 
relation to the origin of the Isopoda and Amphipoda. 
These have also been derived from a shrimp-like 
type, but their possession of a brood-pouch, among 



266 THE LIFE OF CRUSTACEA 

other characters, shows that they are linked on to 
the Mysidacea, and must have arisen from some 
primitive member of that group, like Pygocephalus. 
Although palaeontology as yet gives little help in 
tracing the course of their evolution, we can im- 
agine what the intermediate links must have been 
like by comparison with the living Cumacea and 
Tanaidacea. 

It is possible, indeed, that the divergence of the 
Isopod line of descent from that of the Mysidacea 
took place earlier than the Carboniferous epoch, 
for there has recently been discovered in rocks of 
Devonian age in IrefiMd a single specimen of a fossil, 
to which the name of Oxyuropoda has been given, 
which has every appearance of being an Isopod. 
At all events, undoubted Isopods make their appear- 
ance in rocks of the Secondary Period, and some of 
those from the Jurassic epoch are not very different 
in general form from types still existing. 

Some of the Carboniferous shrimp-like Crustacea 
present characters which seem to point in the direc- 
tion of the Stomatopoda, and fossils which clearly 
belong to that group are found in Jurassic and 
later deposits. In the Cretaceous epoch there were 
Stomatopoda resembling modern types so closely 
that they have been referred to the existing genus 
Squilla. We are even able to say that they resembled 
the living Stomatopoda in their mode of development, 
for larvae of the type known as Erichthus have been 



CRUSTACEA OF THE PAST 267 

recognized in rocks of Cretaceous age from Lebanon. 
This is a striking example of the way in which, by a 
fortunate accident as it were, organisms apparently 
ill-adapted for fossilization may occasionally be pre- 
served. 

Of the Decapoda the geological history is tolerably 
full, and it is possible to trace in its broad outlines 
the course of evolution of the various suborders. 
Here again it is likely that the beginnings of the 
group are to be sought for in the Carboniferous 
epoch, and some of the obscure shrimp-like forms 
of that age show hints of an affinity with the 
Decapods. In the Triassic epoch, however, and 
more abundantly in the succeeding Jurassic, a 
number of types are found which seem to include 
primitive representatives of several of the existing 
groups of Natantia and Reptantia. It is noteworthy 
that among them are some forms (Mger, etc.) 
resembling the existing Stenopidea, a tribe which 
in some respects is intermediate between these two 
suborders. In the Stenopidea the first three pairs 
of legs bear pincer-claws, as in the Lobster, but the 
third pair is much the largest ; and JEger agrees with 
them in this unusual character, though there is little 
else, in what is known of its structure, to help to 
determine its affinities. 

The tribe Penasidea, which occupies in many 
respects a primitive place among the Natantia, is 
abundantly represented in the Jurassic epoch, 



268 THE LIFE OF CRUSTACEA 

especially in the lithographic stone (Upper Jurassic) 
of Solenhofen, and by somewhat doubtful specimens 
from the earlier Trias. All these agree in having 
the first three pairs of legs with pincer-claws, and 
not differing greatly in size. Some of the Jurassic 
and later fossils are of so modern a type that they 
have been referred to the existing genus Penceus. 

The Upper Jurassic rocks also preserve the earliest 
undoubted specimens of true Prawns of the tribe 
Caridea, and some of these show swimming branches 
(exopodites) on the thoracic legs, so that they were 
probably related to the primitive family Acanthe- 
phyridse, of which {he existing members are found in 
the deep sea. It is possible, however, that Caridea 
were already in existence far earlier, for some of 
the obscure Carboniferous forms seem to have the 
broadened side-plates of the second abdominal somite, 
which, so far as we know, are exclusively characteristic 
of that tribe. 

The Reptantia, forming the other large division of 
the Decapoda, also had their origin at least as early 
as the Triassic epoch, where representatives of the 
tribes Eryonidea and Scyllaridea are found. The 
history of the Eryonidea has already been discussed 
(p. 133) in dealing with the deep-sea Crustacea. The 
oldest representatives of the Scyllaridea belong to a 
family (Glyphseidse) now wholly extinct, and are in 
many respects more primitive and lobster-like than 
any of the living Spiny Lobsters and their allies 



CRUSTACEA OF THE PAST 269 

(Palinuridse and Scyllaridae). Forms with greatly 
thickened antennae, indicating a transition to the 
Palinuridae, begin to appear in the Jurassic ; and 
in the later Cretaceous a genus, Podocrates, occurs 
which is hardly to be distinguished from Linuparus, 
now living in Japanese seas. The Scyllaridae have 
the antennae modified into broad shovel-like plates, 
and perhaps take their origin from Cancrinus, in the 
Solenhofen lithographic stone (Jurassic), which has 
broad and apparently flattened antennae. True 
Scyllaridae are certainly found in Cretaceous de- 
posits, and some, from the Upper Chalk, are even 
referred to the existing genus Sc$llarus. 

The Anomura are almost unknown as fossils, but 
the true Crabs, or Brachyura, are abundantly repre- 
sented. They first appear about the middle of the 
Jurassic epoch, and, as already pointed out, the 
earliest forms (Prosoponidae) are referred to the 
Dromiacea, and appear to be closely related to the 
primitive Homolodromiidae now living in the deep sea 
(p. 134). One of the oldest, and at the same time one 
of the most completely known, is Protocarcinus, from 
the Great Oolite of Wiltshire, which is preserved (in 
the only known specimen) with the abdomen partly 
extended, possibly indicating that the abdomen was 
less closely doubled under the body than in modern 
Crabs. 

The next group of Crabs to appear are the Oxysto- 
mata, which are found from the middle of the 



270 THE LIFE OF CRUSTACEA 

Cretaceous epoch onwards. The Brachyrhyncha 
perhaps begin to appear about the same time, but 
the affinities of the earlier types are doubtful, and it 
is only in the Tertiary that they become abundant 
and unmistakable. Several living genera, such as 
Cancer, date back to the Eocene. The Spider Crabs 
(Oxyrhyncha) are rare as fossils, and the earliest 
specimens are found near the beginning of the 
Tertiary. 



APPENDIX 

I. METHODS OF COLLECTING AND PRESERVING 
CRUSTACEA 

IT may be useful to give here a few hints as to the 
methods of collecting Crustacea. Of the species 
that live in the sea, many may be found between tide- 
marks by turning over stones and searching among 
sea-weeds and in rock crevices. A small hand-net, 
made by fastening a bag of coarse muslin to a stout 
wire ring of a few inches diameter, is useful for fishing 
in rock pools. Shore-collecting in this manner is 
most productive at spring-tides, when the deeper 
levels of the shore are open to exploration. 

Many burrowing species are to be found by digging 
in the sand near low-water mark. In addition to 
Crabs and other large species, many minute forms, 
Amphipods, Cumacea, and the like, inhabit such 
localities. The best way of collecting these is to 
stir up a spadeful of the sand in a bucket of water, 
and, after allowing the sand to settle for a few 
seconds, to pour off the water through a muslin bag. 
After repeating the operation two or three times, the 
contents of the bag are washed out into a jar or dish 

271 



272 THE LIFE OF CRUSTACEA 

of sea-water for examination with a lens or under the 
microscope. 

Dredging is the most effective method of obtaining 
Crustacea that live in deeper water. The dredge 
usually employed by naturalists consists of a heavy 
rectangular iron frame to which is attached a strong 
bag-shaped net. The two longer sides of the frame 
are sharp-edged and bevelled outwards, so as to 
"bite" when the dredge is dragged along the sea- 
bottom. To the shorter sides are hinged a pair 
of arms ending in rings. The dredge-rope is made 
fast to one of these rings, while the other is held 
only by a " stopping " of yarn, which gives way if 
the dredge should catch on a rock, and permits it 
to be dragged sideways off the obstruction. The 
size and weight of the dredge may vary according 
to the depth at which it is to be used and the power 
available for working it. A convenient size for use 
with a small sailing boat at moderate depths has 
a frame 20 by 5 inches. 

Apart from dredging, many specimens from 
moderately deep water may be picked out from 
among the " rubbish " brought up on fishermen's 
lines or by the trawl, and various Crustacea besides 
the edible species find their way into Lobster and 
Crab pots. The true deep-sea fauna is, for the most 
part, only to be reached by specially-equipped ex- 
peditions, although specimens from great depths are 
occasionally obtained during the operations for the 
repair of submarine telegraph cables. 

The floating animals of the surface of the sea are 



COLLECTING AND PRESERVING 273 

to be captured by means of the tow-net. This con- 
sists of a conical bag of muslin, cheese-cloth, or, best 
of all, silk " bolting-cloth," attached to a galvanized 
iron ring of one or two feet in diameter, and having 
a zinc can or a strong glass jar fixed to the narrow 
end. The ring is attached by three equidistant cords 
to the towing line, and the net is towed slowly at 
or near the surface of the sea. When taken on 
board, the contents of the can are emptied into a 
jar of sea-water for examination. The tow-net is 
best used when there is only enough way on the 
boat to keep the net from sinking ; if towed more 
rapidly, delicate organisms are apt to be crushed 
by the pressure of the water, or the net itself may 
be burst. The use of unnecessarily fine nets should 
be avoided. A fine-meshed net may not capture a 
single specimen of the larger Crustacea, even though 
these may be swarming in the water through which 
it is drawn. 

By weighting the tow-net it may be used at various 
depths to capture the floating animals of mid-water. 
When it is so used, however, it is impossible to tell 
from what depth any particular specimen may have 
come, since it may have been captured during the 
hauling in of the net. For more precise investiga- 
tions in deep water, " closing tow-nets " of various 
types have been devised, which can be opened by 
a " messenger " sent down the line when the net has 
reached the desired depth, and closed again by 
another " messenger " before it is hauled in. 

A simple method that has proved very successful 
18 



274 THE LIFE OF CRUSTACEA 

for collecting small Crustacea living on a sandy 
bottom in shallow water is to employ a light tow-net 
with a cane ring, and with a heavy sinker attached 
to the towing line at a distance of a few feet in 
front of the net. As the sinker is dragged along 
the bottom, the net floats up behind it, and catches 
small animals stirred up by its passage. 

For collecting the smaller fresh-water Crustacea 
Water-fleas and the like a small muslin ring-net 
may be used in ponds and ditches. The plankton 
of the open water of lakes is best obtained by means 
of a tow-net like that described above for use in 
the sea. 

The interesting blind species known as " Well 
Shrimps " are to be looked for in the water of springs 
and wells. In wells fitted with a pump, Professor 
Chilton found that "the Crustacea are often brought 
up most abundantly when pumping is first com- 
menced, and that jerking the handle of the pump 
somewhat violently is often more successful than 
pumping at the ordinary rate." In disused open 
wells, they may be trapped by baiting a muslin 
ring-net with a piece of stale meat or fish, and 
pulling it up rapidly after it has remained in the 
well for a few hours. The subterranean waters of 
caves have yielded many curious species in various 
parts of the world. For the capture of species 
living in the deep water of large lakes, a special 
form of dredge has been devised with runners to 
prevent it from sinking into the soft mud, while 
the mouth of the net is raised a few inches above 
the bottom. 



COLLECTING AND PRESERVING 275 

For preserving Crustacea the best medium to use 
is 70 per cent, alcohol. Strong spirit diluted with 
a little less than one-third its bulk of water gives 
about the required strength. If too strong spirit 
is used, the specimens tend to be hard and brittle, 
and delicate organisms become shrivelled. Methy- 
lated spirit as sold in the shops in this country 
contains mineral naphtha, and turns milky when 
water is added, so that it is unsuitable for preserving 
specimens. Methylated alcohol without naphtha 
can be bought, by permission of the Inland Revenue 
authorities, but only in considerable quantities at a 
time. 

Formalin is very cheap and readily obtained, but 
it is much less suitable than spirit for most Crustacea, 
as it tends to make them stiff and fragile, and small 
forms containing much lime, such as Cumacea, may 
become decalcified. For Crustacea collected by the 
tow-net, however, formalin gives good results. A 
few drops of strong formalin, added to the water 
into which the tow-net has been washed, kills the 
animals in a few minutes. After they have sunk 
to the bottom, the liquid may be poured off and 
replaced by formalin diluted with sea-water (for 
marine plankton), or by a mixture of formalin and 
spirit. The most suitable strength of formalin varies 
with different organisms, but 5 per cent, (i.e., i part 
of commercial formalin to 19 parts of water) is 
perhaps most generally useful. 

Crabs, Prawns, and the like, if put alive into 
strong spirit, may throw off some of their limbs, 



276 THE LIFE OF CRUSTACEA 

or else become so rigid that these break on the 
slightest manipulation. This may often be avoided 
by killing the animals in weak spirit (30 per cent, or 
less) before preserving in strong spirit. Marine 
species may also be killed by placing them in fresh 
water, care being taken not to allow them to remain 
in it longer than is necessary, as it causes distortion 
of the membranous appendages. 

The larger Crabs, Lobsters, and the like, may be 
preserved dry, although in this state they are 
unsuitable for examination of the more delicate 
appendages. The carapace should be detached, and 
the soft parts cleaned away as far as possible, a 
bent wire being used, if necessary, to remove the 
flesh from the legs. The specimens should be dried 
in the shade, to preserve as much as possible of the 
natural colour. 

With specimens intended for permanent preserva- 
tion in spirit, the use of corks should be avoided, as 
they discolour the spirit, and ultimately the speci- 
mens. Small specimens are most conveniently kept 
in glass tubes closed with a piece of clean elder-pith 
(not cotton-wool), and placed, upside down, in a 
bottle of spirit. Labels to be placed inside the 
tubes are best written with Indian ink, and allowed 
to dry before immersion in the spirit. 



NOTES ON BOOKS 277 



II. NOTES ON BOOKS 

The literature of Carcinology is bewildering in its 
extent, and is for the most part scattered through 
the volumes of scientific periodicals and the publica- 
tions of learned societies in most of the languages of 
Europe. A guide to the current literature is pro- 
vided by the Zoological Record, the latest volume 
of which, relating to the year 1909, enumerates no 
fewer than 337 papers dealing wholly or in part with 
this group of animals. 

The following short list of books in the English 
language may be of some help to the beginner. 
Most of them give references to the literature which 
will provide the necessary guidance towards a further 
study of the subject. 

GENERAL WORK 

Huxley, T. H. The Crayfish : an Introduction to the Study of 
Zoology. International Science Series, vol. xxviii. London, 
1880. 

Stebbing, T. R. R. A History of Crustacea : Recent Mala- 
costraca. International Science Series, vol. Ixxiv. London* 
1893. 

Caiman, W. T. Crustacea. A Treatise on Zoology, edited by 
Sir Ray Lankester. Part vii., fascicle iii. London, 1909. 

Smith, G., and Weldon, W. F. R. Crustacea. The Cambridge 
Natural History, vol. iv. London, 1909. 

Lister,}. J. Crustacea, in "A Student's Textbook of Zoology," 
by Adam Sedgwick. Vol. iii. London, 1909. 



278 THE LIFE OF CRUSTACEA 



BRITISH CRUSTACEA 

Baird, W. The Natural History of the British Entomostraca. 
(Ray Society.) London, 1850. 

Bell, T. A History of the British Stalk-eyed Crustacea. 
London, 1853. 

Spence Bate, C., and Westwood,}. O. A History of the British 
Sessile-eyed Crustacea. 2 vols. London, 1863 and 1868. 

Brady, G. S. A Monograph of the Free and Semiparasitic 
Copepoda of the British Islands. (Ray Society.) 3 vols. 
London, 1878-1880. 

These works, although still valuable, and indeed 
indispensable, are now more or less out of date. A 
list of British Malacostraca (except Amphipoda) 
will be found in Mr. Stebbing's volume mentioned 
above. 

Sars, G. O. An Account of the Crustacea of Norway. Vol. i., 
Amphipoda, 1890-1895. Vol. ii., Isopoda, 1896-1899. 
Vol. iii., Cumacea, 1899-1900. Vols. iv. and v., Copepoda, 
1903 (in progress). Christiania and Bergen. 

A very large proportion of the British species in 
the groups mentioned are described and figured in 
this splendid series of volumes. The text is in 
English. 

Norman, A. M., and Scott, T. The Crustacea of Devon and 
Cornwall. London, 1906. 

Webb, W. M., and Sillem, C. The British Woodlice. London, 
1906. 

Memoirs of the Liverpool Marine Biology Committee, edited 
by Professor W, A. Herdman. A useful series of mono- 



NOTES ON BOOKS 279 

graphs on the structure and life-history of common British 

marine animals and plants. The following relate to 

Crustacea : 
Memoir VI. Lepeophtheirus and Lernaea (Parasitic Copepoda). 

By A. Scott. 1901. 
Memoir XII. Gammarus (Amphipod). By M. Cussans. 

1904. 

Memoir XIV. Ligia (Isopod). By C. G. Hewitt. 1907. 
Memoir XVI. Cancer (Edible Crab). By /. Pearson. 

1908. 
Descriptions of all the British species of Barnacles will be found 

in Darwin 's " Monograph of the Sub-class Cirripedia.'' 

(Ray Society.) 2 vols. London, 1851-1854. 



INDEX 



ABDOMEN of Lobster, 6 

Abyssal fauna of lakes, 185 

Acanthephyridae, 268 

Acorn-shells, 41 

sEga : in Sponges, 210; para- 
sitic on fish, 219 

JEger, 267 

s&glea, 181 

Air-breathing Crabs, 188 

Albunea, 102 

Alcock, A. : on habits of Ocy- 
pode, 105 ; on temperature 
of sea, 120; on eyes of deep- 
sea Crustacea, 124; on colour 
in deep-sea Crustacea, 127 ; 
on luminosity of deep-sea 
Crustacea, 125, 126; on eggs 
of deep-sea Prawn, 130; on 
Nephrops, 132; on habits of 
Ccenobtta, 194, 195 

Allen, E. J., on Mackerel 
fishery, 251 

Alpheidse, 211 

American Lobster, 32 

Amphibious Crustacea, 104, 
188 

Amphipoda, 52 ; seashore, 95, 
107 ; plankton, 145 ; terres- 
trial, 189; fresh-water, 172; 
in Sponges, 210; on Jelly- 
fishes, 212; and Hermit 
Crabs, 215 ; parasitic, 223 ; 
wood-boring, 255 

Amphithoe, 95 

Anaspides, structure and fossil 
allies, 264 

Andrews, C. W. : on Land 
Crabs, 190; on habits of 



Ccenobita, 195 ; on habits of 
Birgus, 197, 198 

Anomalocera, 150 

Anomura, 60 ; fresh-water, 181 

Anostraca, 36 ; habits, 162, 164 

Antennae of Lobster, 8, 14 ; 
use in respiration in Corystes, 
100 ; in Albunea, 102 

Antennule of Lobster, 8, 14 

Ants, Woodlice living with, 
205 

Apseudes, 50 

Apus, 36 ; habitats, 161 ; oc- 
currence in Britain, 162 ; 
habits, 163 ; haemoglobin in, 
165 ; fossil allies of, 260 

Appendages of Lobster, 8 ; of 
Trilobites, 259 

Aratus, 189 

Argulus, 41 

Aristotle on Shrimp living 
with Mollusc, 218 

Armadillidium, 203 

Artemia : larvae of, 81 ; habi- 
tat, 164 

Arthropoda, 2 ; classification, 
204 

Asellus, 172 ; destroying fish- 
ing nets, 253 

Astacidse, 176 

Astacoides, 178 

Astacopsis, 177 ; used for food, 

243 

Astacura, 60 
Astacus : habits, 174 ; young, 

76; distribution, 177; used 

for food, 241 
Asymmetry of Lobster, 29 



280 



INDEX 



281 



Atyidae, 179 ; used for food, 

248 
Autotomy, 113; in Lobster, 30 

Baikal, Lake, 182 

Balanus, 42 ; larvae, 83 ; habits, 
114 ; used for food, 237 ; cul- 
tivated for manure, 250 

Barnacles, 41 ; development, 
83; seashore, 114; of high 
seas, 155 ; on Whales, 
Turtles, and Crabs, 209 ; 
parasitic, on fish, 235 ; used 
for food, 237 ; cultivated for 
manure, 250 ; fossil, 261 

Bathynomus, 131 

Beach- fleas, 107 

Bell, T., on development of 
Land Crabs, 193 

"Berry," Lobster in, 28 

Bipolarity, 132 

Birgus, 94; habits and struc- 
ture, 195 ; breeding habits, 
199. See also Robber Crab 

Bloodvessels of Lobster, 17 

Blue Crab, 249 

Bopyroides, 221 

Bopyrus, 221 

Borradaile, L. A. : on habits of 
Remipes, 102 ; on Huenia, 
no; on larvae of Robber 
Crab, 199 

Bouvier, E. L., on Dromiacea, 

134 

Brachygnatha, 63 
Brachyrhyncha, 64 ; fossil, 270 
Brachyura, 62 ; fossil, 269 
Brain of Lobster, 20 
Branchiopoda, 35 ; larvae, 80 ; 

habitats, 161 ; fossil, 260 
Branchiostegite, 18 
Branchipus, 165 
Branchiura, 41 

Brine Shrimp, 164; larvae, 81 
Brood-pouch of Peracarida, 46 
Brown Shrimp, 244 
Browne, F. Balfour, on Apus 

in Scotland, 162 
Browne, Patrick, on Mountain 

Crab, 193 



Bullen, G. E., on food of 

Mackerel, 251 
Bythotrephes, 168 

Caligidae, 225 

Caligus, 225 

Callianassa, 103 

Callinectes, 249 

Calocalanus, 149 

Cambaroides, 177 

Cambarus : distribution, 177; 

habits, 178 ; blind species, 

185 ; used for food, 243 
Cancer : used for food, 248 ; 

fossil, 270. See also Edible 

Crab 

Cancrinus, 269 
Canthocamptus, 170 ; resting 

stage, 171 
Caprella, 54 

Caprellidae, 55 ; habits, 109 
Carapace of Lobster, 6, 9 
Carcmus : larval stages, 68 ; 

habits, 107. See also Shore 

Crab 

Cardisoma, 191 
Caridea, 59; zoe'a of, 73; fossil, 

268 

Caridina, 248 
Carp-lice, 41 
Caspian Sea, 182 
Caudal fork, 40 
Cephalothorax of Lobster, 8 
Ceratiocaris, 262 
Chalimus, 225 
Chela of Lobster, 12 
Cheliped of Lobster, 8 
Chelonobia, 155, 209 
Chelura, 255 
Cher aps, 177 
Chilton, C., on Woodlice in 

New Zealand, 206 
Chirocephalus, 35, 161 
Chitin, 15 

Chondracanthus, 228 
Chromatophores, 31, no 
Chun, C., on eyes of plankton 

Cnistacea, 154 
Chydorus, 165 
Cirolana, 218 



282 



THE LIFE OF CRUSTACEA 



Cirripedia, 41 ; development, 
82 ; on Whales, 209 ; para- 
sitic, 231 ; fossil, 261. See 
also Barnacles 

Cladocera, 37 ; development, 
80; habits, 165; in plankton 
of lakes, 168 ; absence from 
Tanganyika, 184 

Claspers of Chirocephalus , 35 

Classification of Crustacea, 
table, 34 ; of Decapoda, 
table, 58 

Close time for Lobsters, 239 

Coconut Crab. See Robber 
Crab 

Cocoons of Copepoda, 171 

Ccenobita : habits, 194; respira- 
tion, 195 

Ccenobitidae, 61 ; habits, 194 

Colour of Lobster, 31 ; deep- 
sea Crustacea, 127 ; plank- 
ton Crustacea, 150 ; Bran- 
chiopoda, 165; subterranean 
Crustacea, 187 

Colour-change, no 

Columbus and Gulf - weed 
Crab, 155 

Commensalism, 207 

Conchoderma, 209 

Conchcecia, 144 

Conchostraca, 37; habits, 163 

Convergent evolution, 205 

Copepoda, 40 ; development, 
82 ; of open sea, 140 ; plank- 
ton, 149 ; luminosity, 150 ; 
eyes, 152 ; of fresh water, 
170; of Tanganyika, 184; 
and Hermit" Crabs, 215; 
parasitic, 224; as food of 
Mackerel, 250 

Copilia, 152 

Coral of Lobster, 27 

Corals, Crustacea on, 210 

Coronula, 155, 209 

Corycaeidaa, 152 

Corystes, 99 

Crabs : true, 62 ; sand-burrow- 
ing, 99; of fresh water, 179; 
of Tangan}*ika, 183 ; on 
Corals, 21 1 ; carrying Sea- 



anemones, 215; living with 
Molluscs, 217 ; living in 
Sea-urchin, 218 ; Isopods 
parasitic on, 223 ; Rhizo- 
cephala parasitic on, 231 ; 
used for food, 248 ; fossil, 
269. See also Shore Crab, 
Edible Crab, etc. 
Crangon, 59; habits, 97; fish- 
ery, 244 

Crawfish, Sea-, 59 
Crayfish : young of, 76 ; habits, 
174; distribution, 176; ter- 
restrial, 178, 189; blind, in 
caves, 185; in British Isles, 
241 ; used for food, 241 ; 
disease of, 243 

Cumacea, 48 ; habits, 98 ; of 
deep sea, 129; of plankton, 
141 

Cunningham, ]. T., on de- 
velopment of Land Crabs, 
192 

Cup Shrimps, 245 
Cyamidse, 56; habits, 224 
Cyclops, 40 ; nauplius, 82 ; 
habits, 170 ; resting stage, 
171 ; as host of Guinea- 
worm, 252 
Cymothoa, 220 
Cymothoidae, habits, 218 
Cymothoinae, habits, 220 
Cypris, 38; reproduction, 172 
Cypris stage of Barnacles, 84 ; 

of Sacculina, 233 
Cystisoma, 145 
Cythereis, 38 

Daphnia, 38; development, 81 ; 
habits, 165; in plankton of 
lakes, 1 68 

Darwin, C. : on fresh - water 
fauna, 157, 159; on habits of 
Birgus, 198, 199; on Bar- 
nacles used for food, 237 
Decapoda, 57 ; fossil, 267 
Deep-water Prawn, 246 
Delage, Y., on development of 

Sacculina, 232 
Development of Lobster, 28; 



INDEX 



283 



of Crayfish, 77 ; of River 
Crab, 78 ; of Peracarida, 78 ; 
of Woodlice, 79; of Opossum 
Shrimp, 79; of Cladocera, 
80; of Ostracoda, 81 ; of Cope- 
poda, 82 ; of fresh - water 
Crustacea, 160; of Epicar- 
idea, 223 ; of parasitic Cope- 
poda, 225, 227, 230 ; of 
Rhizocephala, 232 

Diaptomus, 170 

Diastylis, 49 

Diatoms, 139 ; relation to 
Mackerel fishery, 251 

Dichelaspis, 209 

Digestive gland, 17 

Dispersal of fresh-water Crus- 
tacea, 159; of Crayfishes, 174 

Distribution of Woodlice, 206 

Doflein, F., on luminosity in 
marine animals, 126 

Dogfish, Barnacle parasitic on, 

235 

Donppe, 95 
Dracunculus, 252 
Dromia, 63 ; habits, 96 ; and 

Sponge, 215 
Dromiacea, 63 ; of deep sea, 

128, 134 
Dublin Prawn, 33 ; fishery, 240 

Ebalia, 63 ; protective resem- 

, blance, 109 

Ecrevisse, 242 

Edelkrebs, 242 

Edible Crab, 64, 248 

Eggs of Lobster, 27 ; of deep- 
sea Crustacea, 130; of fresh- 
water Branchiopoda, 161 

Endopodite, n 

Eng&us : distribution, 177 ; 
habits, 179, 189 

Entoniscidae, 223 

Ephippium of Cladocera, 167 

Epicaridea, habits, 221 

Epiplankton, 143 

Epipodite, u 

Epistome, 62 

Erichthus larva, fossil, 266 

Eryon, 135 



Eryonidea, 60; eye-stalks of. 
122; luminosity, 126; eggs 
of, 131 ; fossil and living 
species, 133, 268 

Estheria, 36; habitats, 161 

Eucarida, 56 

Eucopepoda, 41 

Eumalacostraca, 45 

Eupagurus, 91 ; commensals, 
213 

Euphausiacea, 56; larvae, 76; 
of deep sea, 124, 125 ; lumin- 
ous organs, 125, 151 ; eyes, 
153 ; fossil, 263 

European Lobster, 32 

Eurydice, 219 

Evolution, 256 

Excretory organs, 19 

Exopodite, 10 

Exoskeleton, 15 

Eyes of Lobster, 20; of Cyclops, 
40; of deep-sea Crustacea, 
121 ; of plankton Crustacea, 
151 ; of Bythotrephes, 169 ; 
degeneration in subter- 
ranean Crustacea, 186 

Eye-stalk of Lobster, 14 

Fairy Shrimp, 35 ; habitats, 

161 

Filaria, 252 
Fiddler Crab : habits, 106 ; 

colour-change, in 
Fish : attacked by Isopods, 

219; Crustacea as food of, 

250 

Fish-lice, 224 
Flagellum, 14 
Foraminifera, 118 
Fossil Crustacea, 256 

Galathea, 130 

Galatheidea, 60 

Galls on Corals, 211 

Gamble, F. W., on colour- 
changes, in 

Gammaridea, eyes of, 154 

Gammarus, 53 ; distribution, 
172 ; in Lake Baikal, 183 

Ganglia of Lobster, 20 



284 



THE LIFE OF CRUSTACEA 



Garstang, W., on habits of 

Masked Crab, 100 
Gastric Mill of Lobster, 17 
Geographical distribution of 

Lobsters, 32 ; of Crayfishes, 

174 

Gecarcinidse, 190 

Gecarcinus, 190 ; supposed me- 
tamorphosis, 192 

Gecarcoidea, 190 

Gelasitmis, 188; habits, 106; 
colour-changes, in 

Generative organs of Lobster, 
27 

Giant Crab, 64 

Giesbrecht on luminosity of 
Copepoda, 150 

Gill chamber of Lobster, 18 

Gills of Lobster, 12, 18; of 
Mysidacea, 48 

Globigerina ooze, 119 

Glomeris, a Millipede, 3, 203 

Glyphasidse, 268 

Gnathobases of Trilobites, 

259 

Gnathophausia, 48 
Goose Barnacle, 42 
Gosse, P. H., on Porcelain 

Crabs, 115 
Grapsidae, 180 
Grapsus, 107 
Green gland, 19 
Gribble, 253 
Guilding, L., on development 

of Land Crabs, 193 
Guinea-worm, 252 
Gulf -weed Crab, 155 ; on 

Turtles, 208 

Habitations of shore Crus- 
tacea, 95 
Hcsmocera, 229 
Haemoglobin in Branchiopoda, 

165 

Hairs of Lobster, 22 

Hall. See Spencer and Hall 

Halocypridae, 141, 144; lumin- 
osity, 151 

Hapalocarcinus, 211 

Head of Lobster, 7 



Hearing, sense of, in Lobster, 

22 

Heart of Lobster, 17 
Hermaphroditism of Cirri - 

pedia, 43 ; in Isopoda, 52 ; 

of Cymothoinae, 221 ; of 

Epicaridea, 223 ; of Rhizo- 

cephala, 231 
Hermit Crabs, 61 ; of seashore, 

91 ; of deep sea, 124, 136 ; 

terrestrial, 194; commensals, 

213 ; Isopods parasitic on, 

221 

Heterocarpus, 125 

Hickson, S. J.,on Caridina, 248 

Hippa, 102 

Hippidea, 62; habits, 102 

Hippolyte, colour-changes, in 

Hotopeditim, 170 

Homaridae, 33 

Homarus, 32 ; fishery, 238 

Homolodromiidse, 134 ; fossil 
allies, 269 

Homologous organs, 10 

Hoplqcarida, 64 

Huenia, 109 

Huxley, T. H. : on Barnacles, 
115; on distribution of Cray- 
fishes, 176 

Hyas, masking habits, 96 

Hyperia, 142; on Jellyfishes, 
212 

Hyperiidea, 141 ; eyes, 154 

Hypoplankton, 143 

Hypostome, 259 

Inachus infected with Saccu- 

lina, 235 

Intestine of Lobster, 16 
Isopoda, 51 ; deep-sea, 131 ; 
fresh - water, 172 ; subter- 
ranean, 186; land, 199; in 
Sponges, 210 ; parasitic, 218 ; 
wood-boring, 253 ; fossil, 266 

Jasus, 241 

Jellyfishes, Amphipods on, 212 

Keeble, F., on colour-changes, 
in 



INDEX 



Kidney, 19 
Koonunga, 264 

Land Crabs, 189 ; injuring 
crops, 253 

Land Hermit Crabs, 194 

Land-hoppers, 189 

Langouste, 241 

Lankester, E. Ray, on haemo- 
globin in Branchiopoda, 165 

Larvae of Lobster, 28 ; of Nor- 
way Lobster, 7 1 ; of Stomato- 
poda, 80; of Brine Shrimp, 
8i ; of Land Crabs, 191 ; of 
Robber Crab, 199; fossil, of 
Stomatopoda, 266 

Larval stages, 66 ; significance 
of, 85 

Latreillia, 128 

Leach, W. E., on the Gribble, 

254 

Leander, 59, 179; Isopod para- 
sitic on, 221 ; used for food, 

245 

Legs of Lobster, 8, 12 

Lepas, 42 ; habitat, 155; nau- 
plius, 148 

Lepeophthirns, 225 

Leptodora, 169 

Leptostraca, 45 

Lerncea, 226 

Leucosiidae, 109 

Ligia, structure and habits, 
200 

Limnoria, 254 

Linuparus, 269 

Lithodes, 62, 94 

Lithodidse, 61 

Liver of Lobster, 17 

Lobsters: deep-sea, 121; fish- 
ery, 238 

Loven, S., on relict Crustacea, 
181 

Luminosity of deep-sea Crus- 
tacea, 125; of plankton Crus- 
tacea, 150 

Lynceidse, 165 

Mackerel feeding on plankton, 
250 



Macropodia, masking habits, 

97 

Maia, masking habits, 96 
Malacostraca, 43 ; fossil, 261 
Mammoth Cave. Crayfish of, 

185 

Mandible of Lobster, 8, 14 
Masked Crab, 99 
Masking of Crabs, 96, 215 
Maxilla of Lobster, 8 ; of Ar- 

gulus, 41 

Maxillipeds of Lobster, 8, ir 
Maxillula of Lobster, 8 
Medusae, Amphipods on, 212 
Megalopa of Shore Crab, 70 
Meganyctiphanes, 56, 151 
Melia, 215 
Mesidotea, 181 
1 Mesoplankton, 143 
! Messmates, 208 
Metamorphosis of Lobster, 28 ; 

of Land Crabs, 791 
Metanauplius of Penceus, 75 
Mimicry, 204 
Mimonectes, 145 
Mitsukuri, K., on cultivation 

of Barnacles, 250 
Mole Crabs, 102 
Monstrillidae, 230 
Moulting of Lobster, 15 ; of 

Woodlice, 206 

Mountain Shrimps, 181; struc- 
ture and fossil allies, 264 
Mouth-frame of Crabs, 62 
Miiller, Fritz : on larval stages 

of Penceus, 73 ; on habits of 

Aratus, 189 
Miiller, O. F., on Nauplius, 

82 

Munida, larva of, 71 
Munidopsis: eyes, 123; eggs, 

130 

Murray River Lobster, 243 
Mussels and Pea Crab, 217 
Myodocopa, 39 
Mysidacea, 46; development, 

79; luminosity, 127; eyes, 

153 ; and Hermit Crabs, 215 ; 

fossil, 263 
Mysis, 47 ; in lakes, 181, 182 



286 



THE LIFE OF CRUSTACEA 



Natantia, 58; used for food, 

243 

Nauplius of Penceus, 73; of 
Crayfish, 79; of Opossum 
Shrimp, 79 ; of Branchio- 
poda, 80; of Cyclops, 82 ; of 
Ostracoda, 82 ; of Barnacles, 
83 ; of Lepas, 148; of Lepto- 
dora, 170; of Sacculina,2^; 
eye, 40 

Nebalia, 44; fossil allies, 261 

Nebaliacea, 44 

Necton, 138 

Nematocarcinidae, 128 

Nephrops, 33 ; larva, 71 ; dis- 
tribution, 132 ; fishery, 240 

Nephropsidea, 33, 60 

Nephropsis, 121 

Neptunus, 156 ; used for food, 

249 

Neritic plankton, 141 
Nervous system of Lobster, 

20 

Niphargus, 184 
Northern Crayfishes, 176 
Norway Lobster, 33; larva, 

7 1 ; fishery, 240 
Norwegian Prawn, 246 
Notostraca, 36 ; habits, 162 

Oceanic plankton, 141 

Octopus preying on Crustacea, 
89 

Ocypode, 188; habits, 104; car- 
nivorous, 195 

Olfactory filaments of Lobster, 
25 

Oniscns, 51 ; structure and 
habits, 201 

Operculata, 43 

Opossum Shrimps, 46 ; de- 
velopment of, 79 

Orchestia, 107 

Orientation, organs of, 24 

Ostracoda, 38; development, 
81 ; luminosity, 127, 151; 
plankton, 144 ; fresh-water, 
172; of Tanganyika, 184; 
fossil, 261 

Ovary of Lobster, 27 



Oxyrhyncha, 64 ; masking 
habits, 96; fossil, 270 

Oxystomata, 63 ; habits, 101 ; 
protective resemblance, 109 ; 
deep-sea, 128; fossil, 269 

Oxyuropoda, 266 

Oyster Crab, 249 

03 sters and Pea Crab, 217 

Paguridea, 61 

Paguropsis and Sea-anemones, 

214 
Palcemon, 1 79 ; used for food, 

248 

Paltzemonetes, 174 
Palinura, 59 

Palinuridae, 241 ; fossil, 269 
Palinurus,\arva of, 72; fishery, 

240 

Palp, 14 
Pandalus, 59, 1 37 ; used for 

food, 245 
Panulirus, 241 
Paracyamus, 55 
Paranaspides, 264 
Paranephrops, 177 
Parapagurus, 124; and Sea- 
anemones, 213 
Parasitism, 208 
Parastacidae, 176 
Parastacus, 178 
Partan, 248 
Parthenogenesis, 163; ofCla- 

docera, 166 ; of Ostracoda, 172 
Pea Crab, 217 
Pedunculata, 43 
Peltogaster, 232 
Penseidea, 59; fossil, 267 
Penceus, 59 ; larvse, 73 ; used 

for food, 247 ; fossil, 268 
Peracarida, 46 ; development, 

78 

Pericardium, 17 

Peripatus, tracheae of, 204 

Peter's stone, 220 

Philomedes, 38 

Phosphorescence. See Lumin- 
osity 

Photophoresof Euphausiacea, 
125 



INDEX 



287 



Phreatoicidea, 173 

Phronima, 154 

Phronimidse, eyes of, 154 

Phtisica, 54 

Phyllocarida, 261 

Phyllosoma, 149 ; of Spiny Lob- 
ster, 72 

Phylogeny, 205, 256 

Pill Millipede, 203 

Pink Shrimp, 137, 245 

Pinnaxodes, 218 

Pinnotheres, 217 ; used for 
food, 249 

Planes, 155 

Plankton, 139 ; of fresh water, 
160; of lakes, 168, 170; rela- 
tion to fisheries, 250 

Platyarthrus, 205 

Platycuma, 129 

Platymaia, 130 

Platytelphusa, 184 

Pleuron, 9 

Podocopa, 39 

Podocrates, 269 

Pollicipes used for food, 237 ; 
fossil, 261 

Polycheles, 133 

Pontonia, 218 

Pontoporeia, 181 

Porcelain Crab : zoea of, 70; 
autotomy, 114 ; feeding, 115 ; 
and Hermit Crabs, 215 

Porcellana : zoea of, 70; au- 
totomy, 114; feeding, 116 

Porcellanidae, 60 

Porcellio, 51 ; structure and 
habits, 202 ; distribution, 
206 

Portunidae : swimming, 90 ; 
sand-burrowing, 99 ; used 
for food, 249 

Potamobiidae, 176 

Potamobius, 174 

Potamon, 180 ; young of, 78 

Prczanaspides, 265 

Prawns, 58 ; luminosity of, 
127 ; of deep sea, 136 ; of 
fresh water, 174, 179; of 
Tanganyika, 183 ; blind, in 
caves, 185 ; in Sponges, 210; 



Isopods parasitic on, 221 ; 

Common, 245 ; used for food, 

245 ; deep-water, 247 ; fossil, 

268 

Prosoponidae, 135, 269 
Protandrous hermaphrodit- 

ism, 221 

Protective resemblance, 108 
Protocarcinus , 269 
Protocaris, 260 
Protopodite, 10 
Protozoea of Petuzns, 75 
Psathyrocaris, 130 
Pseudothelphusa, 193 
Pseudo-tracheae, 202 
Pygidium, 259 
Pygocephalus, 263 
Pylocheles, 94 
Pylochelidae of deep sea, 136 

Recapitulation, theory of, 86 

Red-clawed Crayfish, 242 

Regeneration in Lobster, 30 

Relict faunas, 182 

Remipes, 102 

Reproduction of Cladocera, 
1 66; of Leptodora, 169; of 
Cymothoinse, 220 

Reptantia, 59 

Respiration in sand-burrowing 
Crabs, 99 ; in amphibious 
Crabs, 106 ; in Land Crabs, 
193 ; in Ccenobita, 195 ; in 
Birgus, 196; in Land Iso- 
pods, 20 1, 202, 203 

Resting eggs of Cladocera, 
166; ofCopepoda, 170 

Resting stage of Copepoda, 
171 

Reversal of asymmetry in 
Lobster, 30 

Rhizocephala, 43 ; larvae, 84 ; 
structure and development, 
231 

River Crabs: young of, 78; 
habits and distribution, 180; 
development of, 193 

River Prawns, 179 ; used for 
food, 248 

Robber Crab, 61, 94; habits 



288 



THE LIFE OF CRUSTACEA 



and structure, 195 ; breed- 
ing, 199 

Robertson, David, on habits 
of Crabs, 97 

Rock Lobster. See Spiny 
Lobster 

Rostrum of Lobster, 6 

Sacculina, 23 1 

Salt lakes, Branchiopoda of, 

165 

Sand-burrowing Crustacea, 97 
Sand-hoppers, 52 ; habits, 107, 

189 

Sapphirina, 150 
Sargasso Sea, 155 
Scampo, 240 
Scapellum, fossil, 261 
Scaphognathite, 19 
Schtzopod stage of Lobster, 

7 1 ; of Penanis, 75 
Scylla, 249 

Scyllaridae, fossil, 269 
Scyllaridea, 59; Phyllosoma 

larvae, 149 ; fossil, 268 
Scyllarus, fossil, 269 
Sea-slater, 200 
Sea-anemones : and Hermit 

Crabs, 213 ; carried by Crab, 

215 

Sea-crawfish. See Spiny Lob- 
ster 

Sea-urchin, Crab living in, 
218 

Sedentary Crustacea, 114 

Self-mutilation in Lobster, 30 

Senses of Lobster, 25 

Sergestes, zoea of, 75, 148 

Serial homology, 10 

Sesarma, habits, 180, 189 

Sessile Barnacles, 43 

Sexes of Lobster, 26 

Sexual characters of Crabs 
infected with Sacculina, 235 

Sharks, Barnacle parasitic on, 

235 

Shore Crab, 64 ; larval stages, 
68; habits, 107, 188; in- 
fested by Sacculina, 231 ; 
used for food, 249 



Shrimps, 58; fresh-water, 53, 
172 ; Common, habits of, 97 ; 
protective resemblance, 108; 
living with Mollusc, 218 ; 
fishery, 244. See also Brown 
Shrimp, Pink Shrimp, etc. 

Sight, sense of, in Lobster, 21 

Skeleton Shrimps, 109 

Slaters, 51 ; Sea-, 200 

Sloane, H., on Gulf-weed 
Crab, 155 

Smell, sense of, in Lobster, 24 

Smith, G. : on terrestrial Am- 
phipoda, 189; on develop- 
ment of Sacculina, 233 

Smith, S. I., on habits of Ocy- 4 
pode, 105 

Somites of Lobster. 6, 8 

Southern Crayfishes, 176 

Spencer and Hall on Aus- 
tralian Branchiopoda, 161, 
163 

Sperm-receptacle of Lobster, 

27 
Spider Crabs, 64 ; masking 

habits, 96, 215 ; deep-sea, 128 
Spiny Lobster, 59 ; larva of, 

72; fishery, 240 
Spirontocans, Isopod parasitic 
" on, 221 

: Sponge Crab, 95 
Sponges, Crustacea in, 210 
Spongicola, 210 
Squilla, 64 ; larva of, 80 ; fossil, 

266 

Stalked Barnacles, 43 
Statocyst of Lobster, 24; of 

Mysidacea, 47 
! Statolith, 47 
Stebbing, T. R. R. : on Land 

Crabs, 190 ; on habits of 

Cirolana, 219 
Steinkrebs, 242 
Stenopidea, 59; fossil, 267 
Stenorhynchus, 97 
Sternum, 9 
Stevenson, R., on the Gribble, 

254 

Stomach of Lobster, 16 
Stone Crab, 61, 94 



INDEX 



289 



Stoinatopoda, 64; larvae, 80; 
habits, 104; fossil, 266 

Stridulating organ of Ocypode, 
105 

Subterranean Crustacea, 184 

Swimmerets of Lobster, 6, 10 

Swimming Crabs, 90; sand- 
burrowing, 99 ; used for 
food, 249 

Symbiosis, 207 

Syncarida, 45, 181 ; fossil, 264 

Tail- fan of Lobster, 6 

Talitridae, 107 

Talitrus : habits, 107; terres- 
trial species, 189 

Tanaidacea, 50 

Tanganyika, Lake, Crustacea 
of, 183 

Taste, sense of, in Lobster, 25 

Telphusa, 180 

Telson of Lobster, 6 

Tergum, 8 

Testis of Lobster, 27 

Thalassinidea, 61 ; habits, 103 

Thaumastocheles, 130, 132 

Thompson, J. Vaughan : dis- 
covery of metamorphoses of 
Crustacea, 67 ; on larvae of 
Cirripedia, 83 ; on develop- 
ment of Sacculina, 232 

Thoracica, 43 

Thorax of Lobster 7 

Thread-worms, 252 

Touch, sense of, in Lobster, 22 

Tracheae, 204 

Tracheae, pseudo-, 202 

Trapeziidae, 211 

Triarthrus, 258 

Trilobites, structure and his- 
tory, 258 



Tubicinella, 209 
Turrilepas, 261 

Turtles : Barnacles on, 209 ; 
Gulf-weed Crab on, 209 

Underground Crustacea, 184 
Uropods of Lobster, 6 

Venus's Flower-basket, Crus- 
tacea in, 210 

Water-fleas, 37, 165 

Weismann on parthenogene- 
sis of Cypris, 172 

Well Shrimp, 184 

Westwood, J. O., on develop- 
ment of Land Crabs, 192 

Whales, Barnacles on, 209 

Whale- food, 138 

Whale-lice, 56 ; habits, 224 

White-clawed Crayfish, 242 

Willey, A., on breeding of 
Robber Crab, 199 

Williamson, H. C., on habits 
of Lobster, 25 

Wood-boring Crustacea, 253 

Woodlice, 51 ; development 
of, 79 ; habits and structure, 
199 ; distribution of, 206 ; 
destructive in gardens, 
253 

Worms: and Hermit Crabs, 
215; Copepoda parasitic in, 
230 

Zoe'a of Shore Crab, 69; of 
Caridea, 73 ; of Porcelain 
Crab, 70; of Munida, 71 ; of 
Penceus, 75 ; of Sergestes, 
75' 148 ; of Robber Crab, 
199 



PRINTED BY 

BILLING AND SONS, LTD. 
GUILDFOKD 



\